SpudFiles Wiki - User contributions [en]

BB machine gun

2011-02-15T14:25:50Z

Jackssmirkingrevenge: /* Typical Performance */

A '''BB Machine Gun''' (BBMG) is a device designed to shoot a large volume of small diameter [[ammunition]], typically plastic airsoft or steel BBs. BBMGs are pneumatic guns but unlike single shot [[pneumatic launcher|launchers]] they require a constant gas supply to function. The common use of a large air [[compressor]] restricts mobility for the majority of BBMGs although models using CO2 or HPA systems have been successfully built as portable units.

The basic principle of most BBMGs is the injection of pressurised gas into a chamber full of spherical ammunition, which is agitated and leaves the barrel accordingly.

The principle can be seen in its most basic form, the "cloud" configuration, in [http://youtube.com/watch?v=_GMMbyJbUQM this 1000 frame per second video] by [http://www.spudfiles.com/forums/profile,mode,viewprofile,u,12312.html jor2daje]

Variations of the position of the air inlet and the inclusion of vortex blocks typically aid with reliability and affect rate of fire, however muzzle velocity and energy is not affected.

== Common Designs ==

* A [[Cloud BBMG]] agitates the BBs in the ammunition chamber by means of the air inlet blowing upwards through them. The agitated BBs then get sucked into the [[barrel]] with the outgoing air stream.

* A [[Tee vortex BBMG]] housed inside of the bottom of a [[tee]], uses the air inlet to swirl the BBs around a circular or semi-circular cutout in a block placed in the BB [[chamber]] and out through a BB sized hole in its side leading to the barrel.

* An [[Inline Vortex BBMG]] uses the same [[vortex block]] from above however the block is housed inside a straight pipe. Normally Inline Vortex BBMG's have a spring/plunger system that forces the BB's into the vortex block to allow firing from any angle without agitation.

* A [[Vortex cap BBMG]] works on an identical principle to a vortex block but instead of a cut-out in a block placed within a large BB chamber it uses the circular internals of a pipe endcap in which to swirl the BBs allowing for a smaller diameter chamber. This potentially allows for a smaller overall design as in [http://www.spudfiles.com/forums/rc-p240-vortex-cap-bbmg-p90-t12907.html this example]

== Design Characteristics ==

The performance of a BBMG, as with any gun, depends on specific characteristics.

'''Air supply [[pressure]] and flow'''

Most of the characteristics that make a good pneumatic spudgun also apply to BBMGs. As with any pneumatic gun, reservoir pressure is directly proportional to the [[muzzle velocity]]. As BB chambers tend to be fairly substantial in volume which is effectily [[dead space]], there is considerable pressure loss between the valve and the barrel as the process is analogous to a trying to pour water in a bucket with a hole in it. This can be mitigated by:

- using a high flow valve, forcing air into the chamber at a faster rate than is escaping through the barrel

- using a [[detent]] to hold the projectile at the breech, blocking off the barrel and allowing pressure to build up before it is released

- [http://i164.photobucket.com/albums/u28/hw97karbine/misc/bbstrafer.jpg storing the BBs directly in the pressure chamber], both passing through the valve meaning there is effectively no dead space

- using a smaller BB chamber, though this means a corresponding reduction in ammunition capacity

'''Barrel tightness'''

The BBs should fit the barrel well enough to minimize leakage of air around the projectile ([[blowby]]) but not so tightly that friction is excessive. Even small differences in diameter can have significant effects on performance. An attempt to quantify this power loss was made in [http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=18&t=8544&hilit=4.5mm+5mm this experiment]

Two 15 inch lengths of barrel tubing were used, one was aluminium with an I/D of 5mm, while the other was a straighted piece of coiled copper tubing with an I/D of 4.5mm. The barrels were hooked up to a blowgun attached to a compressor and used to fire lead BBs - with a nominal diameter of 4.5mm - at 100 psi through a chronograph. Over a 5 shot string, the 5mm I/D barrel averaged 242 feet per second, whilst the 4.5mm I/D barrel averaged 279 feet per second. With an average projectile weight of 8 grains, this gives a muzzle energy of 1.04 and 1.38 ft/lbs respectively - a significant power increase of 33% over the wider barrel.

'''Barrel length'''

The longer the barrel, the more time the BB is under the influence of gas pressure and therefore accelerates further. Due to BBMGs usually fed with gas supply massively disproportionate to barrel volume, making normal pneumatic [[Chamber to barrel ratio]] concerns irrelevant. However, there does appear to be a relationship between barrel length and rate of fire in BBMGs, in that a fresh BB is usually not fed into the barrel before the previous BB escapes the muzzle, therefore a longer barrel would tend to reduce rate of fire. If a detent is fitted at the breech, is is possible that the breech is blocked off by a following BB before the previous BB leaves the barrel, at best resulting in lower power and at worst leading to a collision inside the barrel which could lead to damage.

== Typical Performance ==

The rate of fire for the average gun is very high, in the vicinity of 30 to 100 rounds per second (RPS)- 1800 to 6000 rounds per minute, comparable to that of a [http://en.wikipedia.org/wiki/Minigun modern gatling type machinegun].

BBMGs in general are not usually capable of sustained full performance fire as most air sources cannot provide an adequate flow of sufficiently high pressure air. To reduce air consumption, maintain muzzle velocity and to reduce the rate that the ammunition is expended they are typically fired in short bursts lasting a few seconds at most.

'''Airsoft BBMG Performance'''

Airsoft BBMGs are known for their especially high rate of fire. This is in the region of 30 to 115 rounds per second (RPS), 1800 to 6900 rounds per minute. This is useful in Airsoft skirmishes for laying down suppressive fire or clearing out multiple targets up close. Typical projectile speeds of around 250-400 Feet Per Second(FPS) are comparable to higher end Airsoft Electric Guns (AEGs). The advantage of the high ROF is quite clear in skirmishes however the consumption of such a high volume of pellets can be expensive.

Other disadvantages of using BBMGs in airsoft lies in their portability and range. Portability can be fixed by using an external CO2 setup for the gas supply however it can be costly. The other problem of range is due to the lack of a hop-up system which creates backspin on the BB and so increase the distance they can fly. Although possible to add a hop-up they wear down quickly because of the high ROF.

'''Non-Airsoft BBMG Performance'''

These BBMGs are unregulated by airsoft limitations of plastic pellets as they are not intended to be fired at other people.

With 3 foot length of 1/4" OD (3/16" ID) stainless steel tubing, a 120 PSIG 3 gallon shop compressor and firing standard steel BBs, a typical vortex BBMG has a muzzle velocity of about [http://www.inpharmix.com/jps/Jims_chrono.html 330 FPS]. This is about the same as a cheap commercial single shot BB gun. The muzzle energy for an 0.177" metal BB (0.33g) at 330 FPS is 1.2 foot-pounds (1.7J). Despite the relatively low projectile speed, the abrasive effects of a large number of hard BBs striking a target in a short period of time can be quite destructive.

The high ROF can consume pellets at an expensive rate. A six pound container of 6000 metal BBs costs about $15. At 50 RPS that six pound container will last for two minutes of firing.

== Links ==
[http://www.burntlatke.com/bb.html Latke's BBMG]: An excellent write-up on how to build a Vortex BBMG.

[[Category:BB machine gun]]

BB machine gun

2011-02-12T07:26:23Z

Jackssmirkingrevenge:

A '''BB Machine Gun''' (BBMG) is a device designed to shoot a large volume of small diameter [[ammunition]], typically plastic airsoft or steel BBs. BBMGs are pneumatic guns but unlike single shot [[pneumatic launcher|launchers]] they require a constant gas supply to function. The common use of a large air [[compressor]] restricts mobility for the majority of BBMGs although models using CO2 or HPA systems have been successfully built as portable units.

The basic principle of most BBMGs is the injection of pressurised gas into a chamber full of spherical ammunition, which is agitated and leaves the barrel accordingly.

The principle can be seen in its most basic form, the "cloud" configuration, in [http://youtube.com/watch?v=_GMMbyJbUQM this 1000 frame per second video] by [http://www.spudfiles.com/forums/profile,mode,viewprofile,u,12312.html jor2daje]

Variations of the position of the air inlet and the inclusion of vortex blocks typically aid with reliability and affect rate of fire, however muzzle velocity and energy is not affected.

== Common Designs ==

* A [[Cloud BBMG]] agitates the BBs in the ammunition chamber by means of the air inlet blowing upwards through them. The agitated BBs then get sucked into the [[barrel]] with the outgoing air stream.

* A [[Tee vortex BBMG]] housed inside of the bottom of a [[tee]], uses the air inlet to swirl the BBs around a circular or semi-circular cutout in a block placed in the BB [[chamber]] and out through a BB sized hole in its side leading to the barrel.

* An [[Inline Vortex BBMG]] uses the same [[vortex block]] from above however the block is housed inside a straight pipe. Normally Inline Vortex BBMG's have a spring/plunger system that forces the BB's into the vortex block to allow firing from any angle without agitation.

* A [[Vortex cap BBMG]] works on an identical principle to a vortex block but instead of a cut-out in a block placed within a large BB chamber it uses the circular internals of a pipe endcap in which to swirl the BBs allowing for a smaller diameter chamber. This potentially allows for a smaller overall design as in [http://www.spudfiles.com/forums/rc-p240-vortex-cap-bbmg-p90-t12907.html this example]

== Design Characteristics ==

The performance of a BBMG, as with any gun, depends on specific characteristics.

'''Air supply [[pressure]] and flow'''

Most of the characteristics that make a good pneumatic spudgun also apply to BBMGs. As with any pneumatic gun, reservoir pressure is directly proportional to the [[muzzle velocity]]. As BB chambers tend to be fairly substantial in volume which is effectily [[dead space]], there is considerable pressure loss between the valve and the barrel as the process is analogous to a trying to pour water in a bucket with a hole in it. This can be mitigated by:

- using a high flow valve, forcing air into the chamber at a faster rate than is escaping through the barrel

- using a [[detent]] to hold the projectile at the breech, blocking off the barrel and allowing pressure to build up before it is released

- [http://i164.photobucket.com/albums/u28/hw97karbine/misc/bbstrafer.jpg storing the BBs directly in the pressure chamber], both passing through the valve meaning there is effectively no dead space

- using a smaller BB chamber, though this means a corresponding reduction in ammunition capacity

'''Barrel tightness'''

The BBs should fit the barrel well enough to minimize leakage of air around the projectile ([[blowby]]) but not so tightly that friction is excessive. Even small differences in diameter can have significant effects on performance. An attempt to quantify this power loss was made in [http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=18&t=8544&hilit=4.5mm+5mm this experiment]

Two 15 inch lengths of barrel tubing were used, one was aluminium with an I/D of 5mm, while the other was a straighted piece of coiled copper tubing with an I/D of 4.5mm. The barrels were hooked up to a blowgun attached to a compressor and used to fire lead BBs - with a nominal diameter of 4.5mm - at 100 psi through a chronograph. Over a 5 shot string, the 5mm I/D barrel averaged 242 feet per second, whilst the 4.5mm I/D barrel averaged 279 feet per second. With an average projectile weight of 8 grains, this gives a muzzle energy of 1.04 and 1.38 ft/lbs respectively - a significant power increase of 33% over the wider barrel.

'''Barrel length'''

The longer the barrel, the more time the BB is under the influence of gas pressure and therefore accelerates further. Due to BBMGs usually fed with gas supply massively disproportionate to barrel volume, making normal pneumatic [[Chamber to barrel ratio]] concerns irrelevant. However, there does appear to be a relationship between barrel length and rate of fire in BBMGs, in that a fresh BB is usually not fed into the barrel before the previous BB escapes the muzzle, therefore a longer barrel would tend to reduce rate of fire. If a detent is fitted at the breech, is is possible that the breech is blocked off by a following BB before the previous BB leaves the barrel, at best resulting in lower power and at worst leading to a collision inside the barrel which could lead to damage.

== Typical Performance ==

The rate of fire for the average gun is very high, in the vicinity of 30 to 100 rounds per second (RPS), 1800 to 6000 rounds per minute, comparable to that of a [http://en.wikipedia.org/wiki/Minigun Minigun] which clocks in at 33~66 RPS.

BBMGs in general are not usually capable of sustained full performance fire as most air sources cannot provide an adequate flow of sufficiently high pressure air. To reduce air consumption, maintain muzzle velocity and to reduce the rate that the ammunition is expended they are typically fired in short bursts lasting a few seconds at most.

'''Airsoft BBMG Performance'''

Airsoft BBMGs are known for their especially high rate of fire. This is in the region of 30 to 115 rounds per second (RPS), 1800 to 6900 rounds per minute. This is useful in Airsoft skirmishes for laying down suppressive fire or clearing out multiple targets up close. The projectile speeds of around 250-400 Feet Per Second(FPS) are comparable to higher end Airsoft Electric Guns or AEGs. The advantage of the high ROF is quite clear in skirmishes however the consumption of such a high volume of pellets can be expensive.

Other disadvantages of using BBMGs in airsoft lies in their portability and range. Portability can be fixed by using an external CO2 setup for the gas supply however it can be costly. The other problem of range is due to the lack of a hop-up system which creates backspin on the BB and so increase the distance they can fly. Although possible to add a hop-up they wear down quickly because of the high ROF.

'''Non-Airsoft BBMG Performance'''

These BBMGs are unregulated by airsoft limitations of plastic pellets as they are not intended to be fired at other people.

With 3 foot length of 1/4" OD (3/16" ID) stainless steel tubing, a 120 PSIG 3 gallon shop compressor and firing standard copper or steel BBs, a typical vortex BBMG has a muzzle velocity of about [http://www.inpharmix.com/jps/Jims_chrono.html 330 FPS]. This is about the same as a cheap commercial single shot BB gun. The muzzle energy for an 0.177" metal BB (0.33g) at 330 FPS is 1.2 foot-pounds (1.7J). Despite the relatively low projectile speed, the abrasive effects of a large number of hard BBs striking a target in a short period of time can be quite destructive.

The high ROF can consume pellets at an expensive rate. A six pound container of 6000 metal BBs costs about $15. At 50 RPS that six pound container will last for two minutes of firing.

== Links ==
[http://www.burntlatke.com/bb.html Latke's BBMG]: An excellent write-up on how to build a Vortex BBMG.

[[Category:BB machine gun]]

BB machine gun

2011-02-12T07:25:20Z

Jackssmirkingrevenge: /* Design Characteristics */

A '''BB Machine Gun''' (BBMG) is a device designed to shoot a large volume of small diameter [[ammo]], typically plastic airsoft or steel BBs. BBMGs are pneumatic guns but unlike single shot [[pneumatic launcher|launchers]] they require a constant gas supply to function. The common use of a large air [[compressor]] restricts mobility for the majority of BBMGs although models using CO2 systems have been successfully built as portable units.

The basic principle of most BBMGs is the injection of pressurised gas into a chamber full of spherical ammunition, which is agitated and leaves the barrel accordingly.

The principle can be seen in its most basic form, the "cloud" configuration, in [http://youtube.com/watch?v=_GMMbyJbUQM this 1000 frame per second video] by [http://www.spudfiles.com/forums/profile,mode,viewprofile,u,12312.html jor2daje]

Variations of the position of the air inlet and the inclusion of vortex blocks typically aid with reliability and affect rate of fire, however muzzle velocity and energy is not affected.

== Common Designs ==

* A [[Cloud BBMG]] agitates the BBs in the ammunition chamber by means of the air inlet blowing upwards through them. The agitated BBs then get sucked into the [[barrel]] with the outgoing air stream.

* A [[Tee vortex BBMG]] housed inside of the bottom of a [[tee]], uses the air inlet to swirl the BBs around a circular or semi-circular cutout in a block placed in the BB [[chamber]] and out through a BB sized hole in its side leading to the barrel.

* An [[Inline Vortex BBMG]] uses the same [[vortex block]] from above however the block is housed inside a straight pipe. Normally Inline Vortex BBMG's have a spring/plunger system that forces the BB's into the vortex block to allow firing from any angle without agitation.

* A [[Vortex cap BBMG]] works on an identical principle to a vortex block but instead of a cut-out in a block placed within a large BB chamber it uses the circular internals of a pipe endcap in which to swirl the BBs allowing for a smaller diameter chamber. This potentially allows for a smaller overall design as in [http://www.spudfiles.com/forums/rc-p240-vortex-cap-bbmg-p90-t12907.html this example]

== Design Characteristics ==

The performance of a BBMG, as with any gun, depends on specific characteristics.

'''Air supply [[pressure]] and flow'''

Most of the characteristics that make a good pneumatic spudgun also apply to BBMGs. As with any pneumatic gun, reservoir pressure is directly proportional to the [[muzzle velocity]]. As BB chambers tend to be fairly substantial in volume which is effectily [[dead space]], there is considerable pressure loss between the valve and the barrel as the process is analogous to a trying to pour water in a bucket with a hole in it. This can be mitigated by:

- using a high flow valve, forcing air into the chamber at a faster rate than is escaping through the barrel

- using a [[detent]] to hold the projectile at the breech, blocking off the barrel and allowing pressure to build up before it is released

- [http://i164.photobucket.com/albums/u28/hw97karbine/misc/bbstrafer.jpg storing the BBs directly in the pressure chamber], both passing through the valve meaning there is effectively no dead space

- using a smaller BB chamber, though this means a corresponding reduction in ammunition capacity

'''Barrel tightness'''

The BBs should fit the barrel well enough to minimize leakage of air around the projectile ([[blowby]]) but not so tightly that friction is excessive. Even small differences in diameter can have significant effects on performance. An attempt to quantify this power loss was made in [http://www.spudfiles.com/spudtech_archive/viewtopic.php?f=18&t=8544&hilit=4.5mm+5mm this experiment]

Two 15 inch lengths of barrel tubing were used, one was aluminium with an I/D of 5mm, while the other was a straighted piece of coiled copper tubing with an I/D of 4.5mm. The barrels were hooked up to a blowgun attached to a compressor and used to fire lead BBs - with a nominal diameter of 4.5mm - at 100 psi through a chronograph. Over a 5 shot string, the 5mm I/D barrel averaged 242 feet per second, whilst the 4.5mm I/D barrel averaged 279 feet per second. With an average projectile weight of 8 grains, this gives a muzzle energy of 1.04 and 1.38 ft/lbs respectively - a significant power increase of 33% over the wider barrel.

'''Barrel length'''

The longer the barrel, the more time the BB is under the influence of gas pressure and therefore accelerates further. Due to BBMGs usually fed with gas supply massively disproportionate to barrel volume, making normal pneumatic [[Chamber to barrel ratio]] concerns irrelevant. However, there does appear to be a relationship between barrel length and rate of fire in BBMGs, in that a fresh BB is usually not fed into the barrel before the previous BB escapes the muzzle, therefore a longer barrel would tend to reduce rate of fire. If a detent is fitted at the breech, is is possible that the breech is blocked off by a following BB before the previous BB leaves the barrel, at best resulting in lower power and at worst leading to a collision inside the barrel which could lead to damage.

== Typical Performance ==

The rate of fire for the average gun is very high, in the vicinity of 30 to 100 rounds per second (RPS), 1800 to 6000 rounds per minute, comparable to that of a [http://en.wikipedia.org/wiki/Minigun Minigun] which clocks in at 33~66 RPS.

BBMGs in general are not usually capable of sustained full performance fire as most air sources cannot provide an adequate flow of sufficiently high pressure air. To reduce air consumption, maintain muzzle velocity and to reduce the rate that the ammunition is expended they are typically fired in short bursts lasting a few seconds at most.

'''Airsoft BBMG Performance'''

Airsoft BBMGs are known for their especially high rate of fire. This is in the region of 30 to 115 rounds per second (RPS), 1800 to 6900 rounds per minute. This is useful in Airsoft skirmishes for laying down suppressive fire or clearing out multiple targets up close. The projectile speeds of around 250-400 Feet Per Second(FPS) are comparable to higher end Airsoft Electric Guns or AEGs. The advantage of the high ROF is quite clear in skirmishes however the consumption of such a high volume of pellets can be expensive.

Other disadvantages of using BBMGs in airsoft lies in their portability and range. Portability can be fixed by using an external CO2 setup for the gas supply however it can be costly. The other problem of range is due to the lack of a hop-up system which creates backspin on the BB and so increase the distance they can fly. Although possible to add a hop-up they wear down quickly because of the high ROF.

'''Non-Airsoft BBMG Performance'''

These BBMGs are unregulated by airsoft limitations of plastic pellets as they are not intended to be fired at other people.

With 3 foot length of 1/4" OD (3/16" ID) stainless steel tubing, a 120 PSIG 3 gallon shop compressor and firing standard copper or steel BBs, a typical vortex BBMG has a muzzle velocity of about [http://www.inpharmix.com/jps/Jims_chrono.html 330 FPS]. This is about the same as a cheap commercial single shot BB gun. The muzzle energy for an 0.177" metal BB (0.33g) at 330 FPS is 1.2 foot-pounds (1.7J). Despite the relatively low projectile speed, the abrasive effects of a large number of hard BBs striking a target in a short period of time can be quite destructive.

The high ROF can consume pellets at an expensive rate. A six pound container of 6000 metal BBs costs about $15. At 50 RPS that six pound container will last for two minutes of firing.

== Links ==
[http://www.burntlatke.com/bb.html Latke's BBMG]: An excellent write-up on how to build a Vortex BBMG.

[[Category:BB machine gun]]

BB machine gun

2011-02-12T06:21:58Z

Jackssmirkingrevenge: /* Common Designs */

A '''BB Machine Gun''' (BBMG) is a device designed to shoot a large volume of small diameter [[ammo]], typically plastic airsoft or steel BBs. BBMGs are pneumatic guns but unlike single shot [[pneumatic launcher|launchers]] they require a constant gas supply to function. The common use of a large air [[compressor]] restricts mobility for the majority of BBMGs although models using CO2 systems have been successfully built as portable units.

The basic principle of most BBMGs is the injection of pressurised gas into a chamber full of spherical ammunition, which is agitated and leaves the barrel accordingly.

The principle can be seen in its most basic form, the "cloud" configuration, in [http://youtube.com/watch?v=_GMMbyJbUQM this 1000 frame per second video] by [http://www.spudfiles.com/forums/profile,mode,viewprofile,u,12312.html jor2daje]

Variations of the position of the air inlet and the inclusion of vortex blocks typically aid with reliability and affect rate of fire, however muzzle velocity and energy is not affected.

== Common Designs ==

* A [[Cloud BBMG]] agitates the BBs in the ammunition chamber by means of the air inlet blowing upwards through them. The agitated BBs then get sucked into the [[barrel]] with the outgoing air stream.

* A [[Tee vortex BBMG]] housed inside of the bottom of a [[tee]], uses the air inlet to swirl the BBs around a circular or semi-circular cutout in a block placed in the BB [[chamber]] and out through a BB sized hole in its side leading to the barrel.

* An [[Inline Vortex BBMG]] uses the same [[vortex block]] from above however the block is housed inside a straight pipe. Normally Inline Vortex BBMG's have a spring/plunger system that forces the BB's into the vortex block to allow firing from any angle without agitation.

* A [[Vortex cap BBMG]] works on an identical principle to a vortex block but instead of a cut-out in a block placed within a large BB chamber it uses the circular internals of a pipe endcap in which to swirl the BBs allowing for a smaller diameter chamber. This potentially allows for a smaller overall design as in [http://www.spudfiles.com/forums/rc-p240-vortex-cap-bbmg-p90-t12907.html this example]

== Design Characteristics ==

The performance of a BBMG, as with any gun, depends on specific characteristics. For BBMGs, perhaps the most important are;

* Air supply [[pressure]]
* Sustainability of the supply pressure
* Air flow from supply to barrel
* Barrel length
* The fit of the BBs in the barrel

Most of the characteristics that make a good pneumatic spudgun also apply to BBMGs. As with any pneumatic gun, the higher the reservoir pressure and the longer the barrel (up to a point) the greater the [[muzzle velocity]]. Because of the large amount of compressed gas that is wasted in a typical BBMG, the air supply needs to be fairly substantial. For air supplies with a resevoir such as compressors this can mean [[CB ratio]]s of 100:1 to 1000:1. Note that, for a BBMG, the "chamber volume" includes the volume of the compressor's reservoir.

The BBs should fit the barrel well enough to minimize leakage of air around the projectile ([[blowby]]) but not so tightly that friction is excessive. Herewith the result of an experiment in order to quantify performance loss due to leakage around the projectile:

The basic setup was two 15 inch lengths of barrel tubing, one was aluminium with an I/D of 5mm, while the other was a straighted piece of coiled copper tubing with an I/D of 4.5mm. The barrels were hooked up to a blowgun attached to a compressor and used to fire lead BBs - with a nominal diameter of 4.5mm - at 100 psi through a chronograph. Over a 5 shot string, the 5mm I/D barrel averaged 242 feet per second, whilst the 4.5mm I/D barrel averaged 279 feet per second. With an average projectile weight of 8 grains, this gives a muzzle energy of 1.04 and 1.38 ft/lbs respectively - a significant power increase of 33% over the wider barrel.

The chambering and firing of BBs in a cloud BBMG appears to be a coupled process. Usually, when a BB is passing through the barrel the reduced air flow through the gun inhibits the loading of the next BB into the barrel. When the first BB leaves the barrel the increase in air flow "chambers" the next BB. As a result it appears that there is rarely more than one BB in the barrel at a time. This suggests that the muzzle velocity and ROF of cloud BBMGs are linked. The ROF for a gun would appear to be often very close to the reciprocal of the barrel transit time for a BB.

For example, a 3 foot barrel that fires at 300 FPS has an average barrel velocity of ~150 FPS and a transit time of ~20mS. The ROF would be expected to be about 1/20mS = 50 RPS. Design changes that alter the transit time would be expected to also change the ROF. When adding the feeding system of a vortex block this becomes less of a problem because vortex blocks are more of a forced air system rather than a suction system such as cloud BBMGs.

== Typical Performance ==

The rate of fire for the average gun is very high, in the vicinity of 30 to 100 rounds per second (RPS), 1800 to 6000 rounds per minute, comparable to that of a [http://en.wikipedia.org/wiki/Minigun Minigun] which clocks in at 33~66 RPS.

BBMGs in general are not usually capable of sustained full performance fire as most air sources cannot provide an adequate flow of sufficiently high pressure air. To reduce air consumption, maintain muzzle velocity and to reduce the rate that the ammunition is expended they are typically fired in short bursts lasting a few seconds at most.

'''Airsoft BBMG Performance'''

Airsoft BBMGs are known for their especially high rate of fire. This is in the region of 30 to 115 rounds per second (RPS), 1800 to 6900 rounds per minute. This is useful in Airsoft skirmishes for laying down suppressive fire or clearing out multiple targets up close. The projectile speeds of around 250-400 Feet Per Second(FPS) are comparable to higher end Airsoft Electric Guns or AEGs. The advantage of the high ROF is quite clear in skirmishes however the consumption of such a high volume of pellets can be expensive.

Other disadvantages of using BBMGs in airsoft lies in their portability and range. Portability can be fixed by using an external CO2 setup for the gas supply however it can be costly. The other problem of range is due to the lack of a hop-up system which creates backspin on the BB and so increase the distance they can fly. Although possible to add a hop-up they wear down quickly because of the high ROF.

'''Non-Airsoft BBMG Performance'''

These BBMGs are unregulated by airsoft limitations of plastic pellets as they are not intended to be fired at other people.

With 3 foot length of 1/4" OD (3/16" ID) stainless steel tubing, a 120 PSIG 3 gallon shop compressor and firing standard copper or steel BBs, a typical vortex BBMG has a muzzle velocity of about [http://www.inpharmix.com/jps/Jims_chrono.html 330 FPS]. This is about the same as a cheap commercial single shot BB gun. The muzzle energy for an 0.177" metal BB (0.33g) at 330 FPS is 1.2 foot-pounds (1.7J). Despite the relatively low projectile speed, the abrasive effects of a large number of hard BBs striking a target in a short period of time can be quite destructive.

The high ROF can consume pellets at an expensive rate. A six pound container of 6000 metal BBs costs about $15. At 50 RPS that six pound container will last for two minutes of firing.

== Links ==
[http://www.burntlatke.com/bb.html Latke's BBMG]: An excellent write-up on how to build a Vortex BBMG.

[[Category:BB machine gun]]

Fuel meter

2011-02-10T06:07:09Z

Jackssmirkingrevenge: /* Syringe based meter */

A '''fuel meter''', also known as a '''propane meter''', is used to inject a predetermined amount of [[fuel]] gas (usually [[propane]]) into the [[chamber]] of a [[Combustion cannon|combustion]] or [[hybrid cannon|hybrid]]. Any system that injects a known volume of fuel into the gun is a fuel meter. Fuel meters can take a couple of different basic forms.

[[Image:Syringe small.jpg|frame|60cc Syringe and Needle]]
== Syringe based meter ==
The simplest and cheapest fuel meter is a syringe. The syringe is filled from a propane (or [[butane]]) tank by inserting the syringe tip into a suitable sized piece of hose fitted over the tank outlet. When the tank [[valve]] is opened the syringe plunger will move back. The tank valve is closed when the correct amount of fuel is in the syringe. The syringe is removed from the hose and the excess [[pressure]] in the syringe is released to the atmosphere. The syringe now contains the measured volume of fuel at atmospheric pressure. The fuel is injected into the gun's chamber using a needle passed through a small port, or between the cleanout [[adapter]] and cleanout plug. Plastic syringes up to about 60cc are available from well supplied farm supply stores since the syringes are used to give medicines to farm animals. Expect to pay about $2 for a 60cc plastic syringe and perhaps another $1 for a blunt tip needle. Smaller syringes frequently come with printer cartridge ink refil kits.

[http://www.youtube.com/watch?v=0nM603eOQU4 syringe fuel meter video tutorial]

== Ball valve + pressure regulator based meter ==
More complex fuel meters consist of an adjustable [[pressure regulator]] and [[pressure gauge]], connected to two [[ball valve]]s with a length of pipe in between. The volume of this pipe and the pressure of the gas determines the amount of gas injected. The second ball valve is connected to the chamber of the gun.
A fuel meter is operated as follows:
*The regulator is set to a predetermined pressure for the particular meter and chamber size
*The ball valve closest to the regulator is opened, filling the pipe up until the second ball valve with gas at the regulated pressure
*The first ball valve is closed again, closing off the section of pipe between the two valves
*The second ball valve is opened, the pressurized gas inside the meter expands and enters the main chamber
*The second ball valve is closed, and the cannon is ready to fire

The regulator usually only needs to be set the first time, and further fueling can be done simply by opening and closing the two ball valves. A fuel meter provides fast and very consistent fueling, and is the easiest way to use bottled gas for fuel.

It is possible to construct a fuel meter using only a meter pipe, pressure gauge, and two ball valves (with no regulator). This type of meter is less expensive and will provide accurate fueling, but is not as easy to use as a meter setup with a regulator.

===Calculations===

Constructing a fuel meter and determining the correct pressure to use requires a few calculations. First you need to calculate the fuel:air ratio, and from that the amount of fuel needed. These calculations are covered under [[stoichiometry]].

Formulas for fuel meters:

P=pressure in bar, Vf=fuel volume, Vm=meter volume. Any unit of measurement can be used for the volume, as long as the same unit is used throughout. Pressure needs to be converted to bar, if you have the pressure in psi divide it by 14.7.
*P = Vf/Vm
*Vm = Vf/P
*Vf = P*Vm

===Concrete example===

In the example from the stoichiometry article, we found that the fuel volume needed for a 3000 cc chamber is 126 cc. At 1 atmosphere (14.7 psi) of overpressure, we'd need a meter volume of 126 cc. At twice the pressure, we'd need half the volume and so on.

For the example, we decide that meter pressure will be 3 bar. The meter volume required is then 126/3 = 42 cc.

The Fuel Tool (found on Burnt Latke's [http://www.burntlatke.com/calc.html performance calculators page]) automates the fuel meter calculations.

== Needle Valve plus Pressure Gauge ==

[[Image:UL100_sm.jpg|right|thumb|300px|Bernzomatic Torch]]
Another type of fuel meter is simply a needle valve and a low range pressure gauge. The needle valve can be the valve and very small outlet hole in a typical Bernzomatic torch head.

The needle valve is plumbed to the chamber as is the low pressure gauge. To protect the torch and gauge it is a good idea to plumb both through a single small ball valve. To use, the ball valve is opened. Then the needle valve is opened a small amount. When the pressure in the chamber has risen 4% the two valves are closed. Assuming an atmospheric pressure of 14.7 PSI, adding 4% propane will raise the pressure in the chamber by 0.59 PSIG. Since the pressure rise is small, standard 120 or 250 PSIG gauges won't work for this type of meter.

A possible replacement for a low pressure range gauge is a [http://en.wikipedia.org/wiki/Manometer#Liquid_column|"U-tube manometer"]. In this type of pressure gauge the pressure is related to the difference in height of the two columns of liquid. If the U-tube is filled with water, then a 1" difference in height represents a 0.0361 PSI difference in pressure. So, 0.59 PSI would be a 16.3" height difference for the two water columns.

[[Image:Utube.gif|U-Tube Manometer]]
[[Category:Accessories]]

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Chronometer

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#REDIRECT [[chronograph]]

Chronograph

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In the world of devices that launch things at high velocity a '''chronograph''' is a device for measuring a projectile's velocity. This device is sometimes referred to as a "'''shooting chronograph'''".

There are many methods for measuring the speed of a projectile. They range from simply counting how long a round takes to hit the ground after being fired straight up (the "hang time" method) to sophisticated commercial devices that can measure velocities to an accuracy of less than 1% over a range of velocities from a few tens of feet per second (FPS) to several thousand FPS.

== Hang Time Method ==

One method for estimating the [[muzzle velocity]] of a spud gun is to measure the hang time for a spud fired straight up. The "hang time" is the time from when the spud leaves the [[barrel]] until it hits the ground. If there is no air friction, then the speed at which the spud hits the ground is the same as the muzzle velocity. If air friction is neglected, the formula is based on the equation of motion in a uniform gravitational field;

''Muzzle velocity = (1/2)gt''

Where ''g'' is the acceleration due to gravity (32.2 fpss, 9.81m/s) and ''t'' is the time in seconds from firing until the round hits the ground. So, a hang time of 10 seconds would suggest a muzzle velocity of (1/2)(32.2fpss)(10s)=161fps.

Unfortunately, for a typical spud gun, air friction is significant and makes the simple calculation fail miserably. Hang time can be used to estimate the relative muzzle velocity of two guns firing the same [[ammo]] but it can not be used to calculate the actual muzzle velocity.

If the aerodynamic characteristics of the ammo are known then the hang time can be used to estimate the muzzle velocity, such as in the case of a tennis ball, whose Cd (Coefficient of Drag) has been experimentally determined to be about 0.6.

== Commercial Shooting Chronometers ==

There are several commercially available chronograph suitable for use with spud guns. Perhaps the most common is the Chrony® F1, a product of [http://www.shootingchrony.com/ Shooting Chrony Inc.] The F1 sells at retail for $90 and they are frequently available used for a bit less.

The F1 uses optical detectors to detect the passage of the round and the velocity is shown on a digital display.

== PC and Laptop Based Homemade Chronograph ==

It is fairly easy to construct a usable shooting chronograph from readily available parts. If you have access to a PC or laptop then a chronograph is trivial to construct. The PC can be just about any old PC that has a Win98 or later (or about any version of a Mac) operating system. An old PC that has been retired makes an excellent "data acquisition system" for a homemade chronograph.

Since most guns operate in the subsonic to supersonic range any device designed to work with audio signals will have suitable characteristics.

Most PCs and Laptops made in the last 15 years came equipped with a sound card. The sound card is an analog to digital (A/D) and digital to analog (D/A) converter. Sound cards are usually dual channel (left and right stereo channels), sample at up to 48,000 (48KHz) samples per second at 8 or 16 bits resolution per sample. Therefore, the typical sound card is a fairly powerful data acquisition system. It is possible to buy better data acquisition systems (i.e., laboratory grade equipment) but they are expensive. For our purposes, the sound card is more than adequate and readily available.

== Sound Based Homemade Chronograph ==

The simplest way to use the sound card as a chronometer is to just use a microphone to record the sound of the gun firing at a solid target. The audio recording will have a signal at the moment the projectile left the barrel and another when it strikes the target. If the microphone is positioned the same distance from the muzzle and the target then the average velocity of the round is simply the distance from the muzzle to the target divided by the flight time. If the target is reasonably close to the muzzle, within say a few feet, then the average velocity is essentially the same as the muzzle velocity.

There are a couple software packages that are of use in a PC audio based chronograph. [http://audacity.sourceforge.net Audacity] is an excellent freeware sound recording, visualization and analysis package. Audacity can be used to both record the audio and measure the flight time.

[http://talonairgun.com/softchrono/ SoftChrono] is a freeware Windows application specifically designed for using a microphone plus soundcard as a shooting chronograph.

== Optical Input to a Sound Card Based Chronograph ==

Recordings that are somewhat simpler to interpret can be made if the microphone is replaced with a pair of optical detectors such as phototransistors. This optical approach eliminates any possible confusion caused by echoes and gives a signal that is much easier to interpret.

For example, using the setup described [http://www.inpharmix.com/jps/Jims_chrono.html here], the recording below was obtained for the firing of a [[BB machine gun]];
[[Image:long_burst_part.jpg]]

Each pair of peaks represents a single BB passing over the two photo detector gates. The gates were three inches apart and the first gate an inch or two from the gun's muzzle. The velocity of each BB is calculated as the time between peaks (in seconds) divided by the distance between the two gates. Based on this recording, this particular BBMG is firing at about 330 FPS (the velocity varies from round to round) and with a rate of fire of ~4800 rounds per minute.

[[Category:Tools]]

Epoxy

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BB machine gun

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A '''BB Machine Gun''' (BBMG) is a device designed to shoot a large volume of small diameter [[ammo]], typically plastic airsoft or steel BBs. BBMGs are pneumatic guns but unlike single shot [[pneumatic launcher|launchers]] they require a constant gas supply to function. The common use of a large air [[compressor]] restricts mobility for the majority of BBMGs although models using CO2 systems have been successfully built as portable units.

The basic principle of most BBMGs is the injection of pressurised gas into a chamber full of spherical ammunition, which is agitated and leaves the barrel accordingly.

The principle can be seen in its most basic form, the "cloud" configuration, in [http://youtube.com/watch?v=_GMMbyJbUQM this 1000 frame per second video] by [http://www.spudfiles.com/forums/profile,mode,viewprofile,u,12312.html jor2daje]

Variations of the position of the air inlet and the inclusion of vortex blocks typically aid with reliability and affect rate of fire, however muzzle velocity and energy is not affected.

== Common Designs ==

* A [[Cloud BBMG]] agitates the BBs in the ammunition chamber by means of the air inlet blowing upwards through them. The agitated BBs then get sucked into the [[barrel]] with the outgoing air stream.

* A [[Tee vortex BBMG]] housed inside of the bottom of a [[tee]], uses the air inlet to swirl the BBs around a circular or semi-circular cutout in a block placed in the BB [[chamber]] and out through a BB sized hole in its side leading to the barrel.

* An [[Inline Vortex BBMG]] uses the same [[vortex block]] from above however the block is housed inside a straight pipe. Normally Inline Vortex BBMG's have a spring/plunger system that forces the BB's into the vortex block to allow firing from any angle without agitation.

* A [[Vortex cap BBMG]] works on an identical principle to a vortex block but instead of a cut-out in a block placed within a large BB chamber it uses the circular internals of a pipe endcap in which to swirl the BBs allowing for a smaller diameter chamber. This potentially allows for a smaller overall design. It was designed by Gatorlangman AKA DavidVaini.

== Design Characteristics ==

The performance of a BBMG, as with any gun, depends on specific characteristics. For BBMGs, perhaps the most important are;

* Air supply [[pressure]]
* Sustainability of the supply pressure
* Air flow from supply to barrel
* Barrel length
* The fit of the BBs in the barrel

Most of the characteristics that make a good pneumatic spudgun also apply to BBMGs. As with any pneumatic gun, the higher the reservoir pressure and the longer the barrel (up to a point) the greater the [[muzzle velocity]]. Because of the large amount of compressed gas that is wasted in a typical BBMG, the air supply needs to be fairly substantial. For air supplies with a resevoir such as compressors this can mean [[CB ratio]]s of 100:1 to 1000:1. Note that, for a BBMG, the "chamber volume" includes the volume of the compressor's reservoir.

The BBs should fit the barrel well enough to minimize leakage of air around the projectile ([[blowby]]) but not so tightly that friction is excessive. Herewith the result of an experiment in order to quantify performance loss due to leakage around the projectile:

The basic setup was two 15 inch lengths of barrel tubing, one was aluminium with an I/D of 5mm, while the other was a straighted piece of coiled copper tubing with an I/D of 4.5mm. The barrels were hooked up to a blowgun attached to a compressor and used to fire lead BBs - with a nominal diameter of 4.5mm - at 100 psi through a chronograph. Over a 5 shot string, the 5mm I/D barrel averaged 242 feet per second, whilst the 4.5mm I/D barrel averaged 279 feet per second. With an average projectile weight of 8 grains, this gives a muzzle energy of 1.04 and 1.38 ft/lbs respectively - a significant power increase of 33% over the wider barrel.

The chambering and firing of BBs in a cloud BBMG appears to be a coupled process. Usually, when a BB is passing through the barrel the reduced air flow through the gun inhibits the loading of the next BB into the barrel. When the first BB leaves the barrel the increase in air flow "chambers" the next BB. As a result it appears that there is rarely more than one BB in the barrel at a time. This suggests that the muzzle velocity and ROF of cloud BBMGs are linked. The ROF for a gun would appear to be often very close to the reciprocal of the barrel transit time for a BB.

For example, a 3 foot barrel that fires at 300 FPS has an average barrel velocity of ~150 FPS and a transit time of ~20mS. The ROF would be expected to be about 1/20mS = 50 RPS. Design changes that alter the transit time would be expected to also change the ROF. When adding the feeding system of a vortex block this becomes less of a problem because vortex blocks are more of a forced air system rather than a suction system such as cloud BBMGs.

== Typical Performance ==

The rate of fire for the average gun is very high, in the vicinity of 30 to 100 rounds per second (RPS), 1800 to 6000 rounds per minute, comparable to that of a [http://en.wikipedia.org/wiki/Minigun Minigun] which clocks in at 33~66 RPS.

BBMGs in general are not usually capable of sustained full performance fire as most air sources cannot provide an adequate flow of sufficiently high pressure air. To reduce air consumption, maintain muzzle velocity and to reduce the rate that the ammunition is expended they are typically fired in short bursts lasting a few seconds at most.

'''Airsoft BBMG Performance'''

Airsoft BBMGs are known for their especially high rate of fire. This is in the region of 30 to 115 rounds per second (RPS), 1800 to 6900 rounds per minute. This is useful in Airsoft skirmishes for laying down suppressive fire or clearing out multiple targets up close. The projectile speeds of around 250-400 Feet Per Second(FPS) are comparable to higher end Airsoft Electric Guns or AEGs. The advantage of the high ROF is quite clear in skirmishes however the consumption of such a high volume of pellets can be expensive.

Other disadvantages of using BBMGs in airsoft lies in their portability and range. Portability can be fixed by using an external CO2 setup for the gas supply however it can be costly. The other problem of range is due to the lack of a hop-up system which creates backspin on the BB and so increase the distance they can fly. Although possible to add a hop-up they wear down quickly because of the high ROF.

'''Non-Airsoft BBMG Performance'''

These BBMGs are unregulated by airsoft limitations of plastic pellets as they are not intended to be fired at other people.

With 3 foot length of 1/4" OD (3/16" ID) stainless steel tubing, a 120 PSIG 3 gallon shop compressor and firing standard copper or steel BBs, a typical vortex BBMG has a muzzle velocity of about [http://www.inpharmix.com/jps/Jims_chrono.html 330 FPS]. This is about the same as a cheap commercial single shot BB gun. The muzzle energy for an 0.177" metal BB (0.33g) at 330 FPS is 1.2 foot-pounds (1.7J). Despite the relatively low projectile speed, the abrasive effects of a large number of hard BBs striking a target in a short period of time can be quite destructive.

The high ROF can consume pellets at an expensive rate. A six pound container of 6000 metal BBs costs about $15. At 50 RPS that six pound container will last for two minutes of firing.

== Links ==
[http://www.burntlatke.com/bb.html Latke's BBMG]: An excellent write-up on how to build a Vortex BBMG.

[[Category:BB machine gun]]

BB machine gun

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Jackssmirkingrevenge: /* Design Characteristics */

A '''BB Machine Gun''' (BBMG) is a device designed to shoot a large volume of small diameter [[ammo]], typically plastic airsoft or steel BBs. BBMGs are pneumatic guns but unlike single shot [[pneumatic launcher|launchers]] they require a constant gas supply to function. The common use of a large air [[compressor]] restricts mobility for the majority of BBMGs although models using CO2 systems have been successfully built as portable units.

== Common Designs ==

* A [[Cloud BBMG]] agitates the BBs in the ammunition chamber by means of the air inlet blowing upwards through them. The agitated BBs then get sucked into the [[barrel]] with the outgoing air stream.

* A [[Tee vortex BBMG]] housed inside of the bottom of a [[tee]], uses the air inlet to swirl the BBs around a circular or semi-circular cutout in a block placed in the BB [[chamber]] and out through a BB sized hole in its side leading to the barrel.

* An [[Inline Vortex BBMG]] uses the same [[vortex block]] from above however the block is housed inside a straight pipe. Normally Inline Vortex BBMG's have a spring/plunger system that forces the BB's into the vortex block to allow firing from any angle without agitation.

* A [[Vortex cap BBMG]] works on an identical principle to a vortex block but instead of a cut-out in a block placed within a large BB chamber it uses the circular internals of a pipe endcap in which to swirl the BBs allowing for a smaller diameter chamber. This potentially allows for a smaller overall design. It was designed by Gatorlangman AKA DavidVaini.

== Design Characteristics ==

The performance of a BBMG, as with any gun, depends on specific characteristics. For BBMGs, perhaps the most important are;

* Air supply [[pressure]]
* Sustainability of the supply pressure
* Air flow from supply to barrel
* Barrel length
* The fit of the BBs in the barrel

Most of the characteristics that make a good pneumatic spudgun also apply to BBMGs. As with any pneumatic gun, the higher the reservoir pressure and the longer the barrel (up to a point) the greater the [[muzzle velocity]]. Because of the large amount of compressed gas that is wasted in a typical BBMG, the air supply needs to be fairly substantial. For air supplies with a resevoir such as compressors this can mean [[CB ratio]]s of 100:1 to 1000:1. Note that, for a BBMG, the "chamber volume" includes the volume of the compressor's reservoir.

The BBs should fit the barrel well enough to minimize leakage of air around the projectile ([[blowby]]) but not so tightly that friction is excessive. Herewith the result of an experiment in order to quantify performance loss due to leakage around the projectile:

The basic setup was two 15 inch lengths of barrel tubing, one was aluminium with an I/D of 5mm, while the other was a straighted piece of coiled copper tubing with an I/D of 4.5mm. The barrels were hooked up to a blowgun attached to a compressor and used to fire lead BBs - with a nominal diameter of 4.5mm - at 100 psi through a chronograph. Over a 5 shot string, the 5mm I/D barrel averaged 242 feet per second, whilst the 4.5mm I/D barrel averaged 279 feet per second. With an average projectile weight of 8 grains, this gives a muzzle energy of 1.04 and 1.38 ft/lbs respectively - a significant power increase of 33% over the wider barrel.

The chambering and firing of BBs in a cloud BBMG appears to be a coupled process. Usually, when a BB is passing through the barrel the reduced air flow through the gun inhibits the loading of the next BB into the barrel. When the first BB leaves the barrel the increase in air flow "chambers" the next BB. As a result it appears that there is rarely more than one BB in the barrel at a time. This suggests that the muzzle velocity and ROF of cloud BBMGs are linked. The ROF for a gun would appear to be often very close to the reciprocal of the barrel transit time for a BB.

For example, a 3 foot barrel that fires at 300 FPS has an average barrel velocity of ~150 FPS and a transit time of ~20mS. The ROF would be expected to be about 1/20mS = 50 RPS. Design changes that alter the transit time would be expected to also change the ROF. When adding the feeding system of a vortex block this becomes less of a problem because vortex blocks are more of a forced air system rather than a suction system such as cloud BBMGs.

== Typical Performance ==

The rate of fire for the average gun is very high, in the vicinity of 30 to 100 rounds per second (RPS), 1800 to 6000 rounds per minute, comparable to that of a [http://en.wikipedia.org/wiki/Minigun Minigun] which clocks in at 33~66 RPS.

BBMGs in general are not usually capable of sustained full performance fire as most air sources cannot provide an adequate flow of sufficiently high pressure air. To reduce air consumption, maintain muzzle velocity and to reduce the rate that the ammunition is expended they are typically fired in short bursts lasting a few seconds at most.

'''Airsoft BBMG Performance'''

Airsoft BBMGs are known for their especially high rate of fire. This is in the region of 30 to 115 rounds per second (RPS), 1800 to 6900 rounds per minute. This is useful in Airsoft skirmishes for laying down suppressive fire or clearing out multiple targets up close. The projectile speeds of around 250-400 Feet Per Second(FPS) are comparable to higher end Airsoft Electric Guns or AEGs. The advantage of the high ROF is quite clear in skirmishes however the consumption of such a high volume of pellets can be expensive.

Other disadvantages of using BBMGs in airsoft lies in their portability and range. Portability can be fixed by using an external CO2 setup for the gas supply however it can be costly. The other problem of range is due to the lack of a hop-up system which creates backspin on the BB and so increase the distance they can fly. Although possible to add a hop-up they wear down quickly because of the high ROF.

'''Non-Airsoft BBMG Performance'''

These BBMGs are unregulated by airsoft limitations of plastic pellets as they are not intended to be fired at other people.

With 3 foot length of 1/4" OD (3/16" ID) stainless steel tubing, a 120 PSIG 3 gallon shop compressor and firing standard copper or steel BBs, a typical vortex BBMG has a muzzle velocity of about [http://www.inpharmix.com/jps/Jims_chrono.html 330 FPS]. This is about the same as a cheap commercial single shot BB gun. The muzzle energy for an 0.177" metal BB (0.33g) at 330 FPS is 1.2 foot-pounds (1.7J). Despite the relatively low projectile speed, the abrasive effects of a large number of hard BBs striking a target in a short period of time can be quite destructive.

The high ROF can consume pellets at an expensive rate. A six pound container of 6000 metal BBs costs about $15. At 50 RPS that six pound container will last for two minutes of firing.

== Links ==
[http://www.burntlatke.com/bb.html Latke's BBMG]: An excellent write-up on how to build a Vortex BBMG.

[[Category:BB machine gun]]

Main Page

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Jackssmirkingrevenge: /* External links */

== The Spudding Handbook ==
Welcome to The Spudding Handbook! This wiki format handbook contains all of the information you will ever need to build spudguns, and much more besides. The purpose of this handbook is to explain the principles of spudguns and how they are built and operated. All of the information contained in this handbook is free and available to anybody who wishes to view it.

Look around and enjoy your stay.
--[[User:BC Pneumatics|BC Pneumatics]] 02:13, 31 May 2008 (EDT)
[[Image:Cannon.jpg|frame|An Advanced Combustion Cannon]]
==What is a Spudgun?==
''Main article: [[What_is_a_spudgun%3F|What is a spudgun?]]''

There are many different names for spudguns. They are called potato cannons, spud launchers, potato guns, spud cannons, and a host of others. Whatever you decide to call it, all of the aforementioned describe the same type of device: a device used to accelerate a [[potato]] down the [[barrel]], and launch it some distance. While it may offend some purists, the humble little potato is quickly losing favor to other ammunitions such as [[golf ball]]s, [[tennis ball]]s, and other cheap, uniform projectiles.

==Types of Spudguns==

=== [[Pneumatic_launcher|Pneumatic Launchers]] ===

These use the energy stored in compressed gas to launch a projectile. The launcher's [[chamber]] is [[pressure|pressurized]] and the gas held back from the barrel by a [[valve]]. When the valve is opened the gas is allowed to rapidly expand and escape down the barrel forcing the projectile out before it.

=== Combustion Launchers ===

* '''[[Combustion_launcher|Regular Combustions]]'''

These find the energy needed to launch a projectile from the [[Combustion process|combustion]] of a gaseous [[fuel]] and air mixture. The fuel is added to the air already in the chamber, the chamber is sealed and the mixture ignited. This combustion creates a pressure spike that forces the projectile out through the connected barrel.

* '''[[Hybrid_launcher|Hybrid Launchers]]'''

Hybrid launchers are a special type of combustion launcher that use a pre-pressurized fuel/air mixture. This results in a higher pressure and hotter combustion on ignition, thereby transferring more energy to the projectile.

=== [[BB Machine Gun]]s ===
A [[BB Machine Gun]] (BBMG) is a device designed to shoot a large volume of small diameter ammo, typically plastic airsoft or steel BBs. BBMGs are pneumatic guns but unlike single shot launchers they require a constant gas supply to function.

==Important & Related Links==

[[Index|Glossary/Index]]

[[Good technical examples & articles]]

[[Useful construction links]]

[[Launcher configuration]]

[[Computer Applications]]

[[IPLA|International Potato Launching Association]]

[[Safety]]

[[Ammunition]]

[[Legal issues]]

[[History]] (A Brief History of Spud Guns)

[[SpudFiles forum guidelines]]

[[Spudding Jokes]]

[[Forum Stickies]] (Some of the most important topics on Spudfiles)

==External links==

*[http://en.wikipedia.org/wiki/Spud_gun Wikipedia's page on spudguns]
*[http://www.thehalls-in-bfe.com/GGDT Gas Gun Design Tool, simulation program for pneumatic guns]
*[http://www.thehalls-in-bfe.com/HGDT Hybrid Gun Design Tool, simulation program for hybrid/combustion guns]
*[http://www.spudfiles.com/forums/viewtopic.php?p=13324#13324 ATF Correspondence concerning spud gun legality]
*[http://www.spudfiles.com SpudFiles Forum (aka The Spud Cannon Database)]

History

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A Brief History of Spud Guns

== '''Version 1:''' ==

A long time ago, fabled to be about 40 years, somewhere (in America of course) some middle-aged guys were bored so gathered up a bunch of beer cans (they were steel back then), duct tape, gasoline, and at least one tennis ball. Both ends of all cans were removed save one, from which only the bottom was removed; the peel-top hole end was left as is.

Legend has it that it was suggested that if all these cans were securely taped together to make a long tube, the tennis ball could be stuck down it muzzle loader style and fired by putting a small amount of gasoline in the bottom can (with the hole lid as the breech) and one brave soul (the one that had consumed the most beers) holding a lit match or lighter near the peel-top hole. Miraculously the tennis ball was expelled with great velocity. Much whooping and hollering ensued, and the device was promptly reloaded to verify the first shot was not a fluke. Hence the backyard cannon was born.

The earliest recorded use of actual potatoes being fired from a pneumatic cannon involves the British World War 2 [http://en.wikipedia.org/wiki/Holman_Projector Holman Projector], a pneumatic device mounted on convoy vessels intended to project hand grenades which would deter enemy aircraft from coming too close. In moments of boredom these devices were loaded with potatoes and [http://www.naval-history.net/WW2Memoir-RussianConvoyCoxswain03.htm used for impromptu wargames] with friendly ships as referenced:

"The twin Lewis which had been on top of the casing aft, had been taken away, and in its place was a new weapon, a Holman Projector, a steam-powered piece of equipment not unlike a bit of fall pipe that comes down from the guttering of a house to allow the rain to find its way to the drains.

We were to find out that this was all that it was fit for. Its crew was supposed to put down this pipe an ordinary hand grenade which nestled in a tin; the lever from the grenade came through a slot in the metal container and was held down by a pin in the safe position on the outside of the container. The drill was that when the crew were going to fire this 'thing', first they had to make quite certain that there was enough steam pressure on the gauge to project the grenade out of the pipe. They then took the pin out of the grenade, dropped the grenade still in its container down the spout of the pipe, banging their foot down on a pedal at the base of the pipe, and at the same time aiming the 'gun' at the target. If the target was a plane, the grenade was supposed to go off in the vicinity of the plane after parting company with the container as it left the mouth of the pipe. In theory I suppose that this was quite a legitimate description of its action if the steam pressure applied to the projector was correct; if it wasn't, the grenade and its container had a nasty habit of just managing to climb out of the end of the pipe, and dropping onto the deck where they separated, rolling about until they either exploded where they were, and fragmented amongst those of the crew who were panicking to throw them over the side, or in the sea out of harm's way if the crew had been successful in doing what they had set out to do.

''Most ships' crews found as time passed by that the best use for the Holman Projector was for throwing potatoes or empty cans at their 'chummy ships' as they passed by them in a channel''. To be used for the job for which it was really intended was thought to be more dangerous to those actually firing it than to the aircraft supposed to be at the receiving end. Eventually, I believe, these Holmans were taken off most if not all ships."

== '''Version 2:''' ==

It appears that Alessandro Volta (as in Volt) built the first electrically fired combustion "spud gun" in the 1780's;

<blockquote>The "electric-phlogopneumatic" pistol was thought up by Volta. It was generally filled with a mixture of hydrogen and air, and then corked up. One of the electrodes was touched with one hand; the other hand touched one of the poles of an electrostatic machine. When the spark went off between them and also inside the pistol, a loud explosion resulted which violently shot out the cork. As Volta himself wrote, these experiments "'''stupefied the ordinary observer, caused considerable satisfaction among amateurs and those in the know, for these are experiments combining electricity and inflammable air'''". They responded to the double requirement, which was popular at the time, of "being showy" and of popularizing the latest scientific results.</blockquote>
(from [http://ppp.unipv.it/Volta/Pages/eF5struF.html], see also [http://physics.kenyon.edu/EarlyApparatus/Static_Electricity/Voltas_Pistol/Voltas_Pistol.html] and [http://www.thebakken.org/artifacts/Voltapistol.htm])

Apparently, even eighteenth century scientists enjoyed launching random things, with accompanying loud noises, for the shear joy of doing it. So spudders, when asked, you can describe your hobby as "Following in the footsteps of great scientists like Alessandro Volta".
--[[User:Jimmy101|Jimmy101]] 13:11, 10 May 2007 (EDT)

History

2010-12-13T12:51:24Z

Jackssmirkingrevenge: /* Version 1: */

Burst disk

2010-12-13T12:37:39Z

Jackssmirkingrevenge:

[[Image:Burstdisk.png|frame|Cross-section of burst disk in a union; A is chamber, B is barrel, C is the fragile disk, and D is the union.]]
A '''burst disk''' consists of a thin disc of airtight material that will rupture at a certain pressure, held in place inside a [[union]] or cam lever coupling. (See the [[burst disk material]] page.)

Since the burst disk ruptures almost instantly when the pressure gets to a certain point, they have the fastest [[opening time]] of any [[valve]] in existence, short of a "valveless" launcher. Since they are pressure-triggered they are nearly always used in [[hybrid cannon|hybrids]], they are also occasionally used as the main valve in a [[pneumatic cannon]] because of their superior performance. Sometimes they are used as a secondary valve in a [[pneumatic cannon]] to compensate for the slower opening time of the main valve.

Burst disks are a very close rival to a [[ball valve]] in cost, at roughly $13 for a 2" [[union]] in sch 40 PVC. More expensive (but convenient) devices exist, such as [[camlock coupling]]s.

To use, [[solvent welding|solvent weld]] your chamber to one half of your union or cam coupling. One then 'loads' the valve by putting one or more layers of [[burst disk material]] (such as aluminum foil, or a piece of a beverage container) in between the two halves of the union or coupling. The union or cam coupling is then tightened down, locking the burst disk in place.

In a hybrid cannon, burst disks fail when the pressure builds due to the combusting gases. Prior to this, the chamber was containing the flammable gases at a relatively low pressure. They are also sometimes used on [[combustion cannon]]s - for their noisemaking capabilities, and/or their ([http://www.advancedspuds.com/burstdisk.htm debated]) performance improvement.

In a pneumatic cannon, they can be used in the same way, simply pointing the cannon in the correct direction and filling it until it fires. However, many opt to use another system because of the inherent safety issues with this. Such systems include puncturing it with a pointy object (such as a nail) attached to the end of the projectile, melting it with an electrically heated wire, or having a pneumatically [[triggered burst disk]] system using dual burst disks.

Since Burst disks only last for a single shot and need to be replaced before each round, [[Burst Disk Cartridge]]s (BDC) have been created.

[[category:valves]]

Combustion cannon

2010-12-13T12:27:25Z

Jackssmirkingrevenge: /* Operation & Theory */

[[image:Basic_combustion.JPG|right|thumb|350px|Basic combustion cannon]]
A '''combustion cannon''' is a cannon powered by the combustion of flammable fuel-air mixtures. A basic combustion cannon is the simplest one to build, and is therefore often the choice for first time builders, though advanced designs with more power and usability are also possible. Most of the combustion spudguns are made out of [[PVC]] or [[ABS]].

Though being the simplest cannon of all, a well-made pneumatic or hybrid is usually more powerful then a combustion. The pressures in a combustion usually do not rise above 50-60 psi on [[spray and pray]] cannons and about 70-90 psi on advanced cannons. Jimmy101, a member of spudfiles showed that in closed chamber experiments the maximum pressure possible with a propane mix is a little more then 100psi in a closed chamber.

Potato guns are often painted to increase their aesthetic value and to cover unsightly primer stains. Krylon Fusion, a type of paint specifically made for plastics, is the most common type of spray paint used on potato cannons. Some combustion cannons have chambers made from clear pvc, this allows you to see the internals like the sparks and the fan (LED fans can be beautiful this way) and most importantly: a flash of fire on ignition.

==Basic elements==

* Combustion [[Chamber]]
* [[Fuel]]
* [[Ignition source]]
* [[Barrel]]

==Operation & Theory==

In order to fire, the operator loads a projectile (usually a potato) down into the barrel, adds [[fuel]] to the combustion chamber, like spraying [[aerosol]]s in the back end and screwing the cap on and then triggers the [[ignition source]] (e.g. a piezoelectric [[BBQ ignitor]]). The ignition system creates a spark in the chamber which ignites the fuel. The fuel quickly burns up and the hot gases want to expand, creating pressure. The pressure acts as force on the back of the projectile and pushes it rapidly down the barrel. Muzzle velocity and distance vary greatly mostly depending on the [[stoichiometry]] of the fuel/air mixture, the size and [[chamber to barrel ratio]] (C:B ratio) of the launcher and possible performance increasing additions like a [[chamber fan]].

The most basic spudguns use aerosols like hairspray, deodorant or [[starting fluid]] sprayed in at the back ([[spray and pray]]), while more advanced cannons usually use [[propane]] injection. Besides the difference of low-power aerosols and pure fuels like propane there is not much of a difference between fuels, the power of propane and butane vary no more then a few percent. Achieving the right stoichiometry (right amount of fuel and air/oxygen) is usually more important for the performance. Spray and pray cannons often have poor stoichiometry and thus inconsistent shots with relatively low power. Fast burning fuels like [[hydrogen]], [[acetylene]] and [[oxygen enriched]] mixtures are usually avoided, even if they may be a little more powerful, their fast burn rates and high chance of [[DDT]] create shockwaves that are powerful enough to rip any PVC or ABS chamber to shreds.

The ignition and combustion sequence in a clear barrel/chamber tennis ball launcher can be observed at various speeds in the videos below:

*[http://www.youtube.com/watch?v=lyqHUM0Aj2k real time]

*[http://www.youtube.com/watch?v=CyaMRqjAfKo&feature=related 420 frames per second]

*[http://www.youtube.com/watch?v=6-sahz_GAQE&feature=related 1000 frames per second]

==Advanced improvements==

*[[Chamber fan]]
*[[Stun gun]], [[Flyback circuit|flyback transformer]] or [[camera flash]] ignition
*Multiple [[spark gap]]s
*[[Fuel meter]]
*A good [[C:B ratio]]
*[[Breech loading]] mechanism

The above improvements will increase the power and/or usability of the gun. View those pages for more information.

==Safety==
Non [[pressure rated]] "DWV" pipe is used so now and then in combustion cannons and it is generally accepted that this is safe with basic spray and pray; however some of these cannons have blown up. If you want to be safe you should definitely use pressure rated pipe and fittings, especially on advanced combustions.
As stated above specific fuels such as acetylene, hydrogen, and any oxygen enriched mixtures are not safe to use in a gun made out of PVC or ABS.
When using a normal fuel, pressure rated pipe and fittings and have properly [[solvent welding|solvent welded]] all of the joints, you can be considered 100% safe.

Some people, like parents, think it is unsafe because it is an "explosion" and thus dangerous. In that case point them on the facts that it is just a [[deflagration]] and not a [[detonation]] creating no huge shockwaves, but creating just heat and pressure. This pressure is lower then the rated pressure of pressure rated pipe and fittings and that means the gun simply can't explode.

Note that cold weather makes pvc brittle and you should not use a frozen gun. However a gun that has been frozen some time but is up to normal temperature again is safe to use.
Dropping the gun isn't recommended, especially frozen guns, since this might create tiny cracks; a starting point for completely cracking open and blowing up.

==Legality==
Laws are different in each country, state or even city, check the [[legal issues]] page for more information. In some countries combustion cannons are illegal while pneumatics (possibly being way more powerful) may be legal.

Pneumatic cannon

2010-12-13T12:19:26Z

Jackssmirkingrevenge: /* Common types of launchers */

[[image:pneumatic ballvalve cannon.jpg|right|thumb|300px|Pneumatic ball valve cannon]]
A '''pneumatic cannon''' is a cannon powered by pressurized gas, usually air or CO2. They generally require a little more work to build than [[combustion cannon]]s, but using typical compressor pressures and a decent valve, they will outperform most combustion launchers of the same size.

==Basic Elements==

Pneumatic launchers consist of five basic elements:

*Compressed gas storage reservoir ([[chamber]] for short)
*Filling valve (bicycle [[Schrader valve]]s, [[quick disconnect]]s, etc.)
*Firing valve ([[ball valve]]s, [[sprinkler valve]]s, [[piston valve]]s, bolt-style valves(see piston valves) [[quick-exhaust valve]]s, and [[burst disk]]s are the most common)
*[[Barrel]]
*[[Pressure gauge]] (for safety & repeatable launches)

==Operation & Theory==

In order to fire, the operator loads a projectile into the barrel, fills the chamber with a compressed gas (see [[Pneumatic air sources]] for common filling methods), and activates the main valve thus dumping the air in the chamber to the barrel.

The expansion of the compressed gas propels the projectile down the barrel. The barrel length determines the amount of time the projectile has to accelerate and ultimately the velocity of the projectile.

Higher performance launchers use techniques such as:
* Faster valve opening times - see [[sprinkler valve modification]]
* Higher flow valves to maximize the airflow through the valve (Especially true for cannons with very long barrels)
* Using higher gas pressures.

Less common, but also effective in increasing power, some people will also use a gas with a higher speed of sound and particle speed (e.g. helium).

Efficiency of a cannon can be roughly determined by observing how much noise it makes when fired. A relatively quiet gun is often efficient, as there is little energy left over to create sound.

==Common types of launchers==

'''Ball Valve Launchers'''

Ball Valve Launchers release pressurized gas by way of a ball valve. These valves can be made of metal or plastic, and are available in many sizes and pressure ratings. Ball valves are simple to operate, and have very high flow. However, their opening times are comparitively long compared to other valves such as piston valves. Ball valves are typically used in simple designs, or on launchers with long barrels where large airflow is crucial. They can also be used as breech loaders, or venting ports on combustion cannons.

'''Sprinkler Valve Launchers'''

Sprinkler Valve Launchers release air using a commercially manufactured sprinkler valve. These valves are simple to use and install, but are designed to open slowly. This is due to their main application in water systems, to prevent water hammer from destroying the valve. Since air is being used, one can modify the valve to actuate faster, using a larger pilot valve, such as a blowgun, without fear of hammer effects. Sprinkler valves are the most cost-effective option if a design calls for moderate performance. However, their relatively low flow rates and number of internal bends cause the performance to reduce to roughly 60% of that of a piston valve of the same diameter. Sprinkler valves are typically rated to ~120 psig, but it is unadvisable to use them at this pressure, as they are designed for use with water.

'''Piston Valve/Diaphragm Launchers'''

[[Piston valve]] launchers use a [[piston]] in a valve that either seals against the barrel or chamber. Releasing air through the [[pilot valve]] will cause the remaining air to push the piston away from its sealing position and air will go out the barrel.

This is generally an efficient type of launcher, as the opening time is extremely fast and there is very little constriction of airflow in the actual valve. The only real loss of flow can be attributed to the bends inherent in the design that cause gasses to lose energy as they change direction.

A diaphragm launcher operates on the same principles as a piston valve. The only difference is that the piston cylinder is replaced by a flexible diaphragm that flexes towards the pilot valve to release air into the barrel. These valves open faster than piston valves, but have slightly lower flow rates. While piston valves require a bumper to protect the piston housing, diaphragm valves do not.

'''QEV Launchers'''

[[QEV]] launchers use a similar principle as the [[Piston valve]] only these can be bought from the store. These valves open even faster than piston valves because their [[pilot volume]] is much lower, and the valve is commercially manufactured and optimized.

'''Valveless Launchers'''

"Valveless" launchers do not have conventional valve, rather the projectile itself is held in the barrel sealing off the pressure chamber, and is fired by physically releasing the projectile. Another variation of the theme is to have the projectile held in a seal that will only release the projectile once a certain pressure is reached. This allows the use of a relatively inefficient slow/low flow valve to fill to the required, while still having maximum performance for the given parameters (zero "opening time" with instantaneous full flow) exceeding any other form of mechanical valve.

==Related Links==

Downloading the [[GGDT]] (Gas Gun Design Tool) is highly recommended to those interested in pneumatic launchers.

A page on sprinkler valves and a PDF book can be found here;
[http://www.spudfiles.com/spud_wiki/index.php/The_Sprinkler_Valve The Sprinkler Valve]