SpudFiles Wiki - User contributions [en]

Hgdt

2011-11-04T04:37:17Z

Fnord: Created page with "Hall Consulting's '''Hybrid Gun Design Tool''' is a simulation program to aid the design of combustion cannons and hybrid cannons. It is available [http://www.thehalls-in..."

Hall Consulting's '''Hybrid Gun Design Tool''' is a simulation program to aid the design of [[combustion cannon]]s and [[hybrid cannon]]s. It is available [http://www.thehalls-in-bfe.com/HGDT here].

==Common problems for first time users==
Read, and follow, the [http://thehalls-in-bfe.com/HGDT/installation.html installation instructions] for HGDT before installing.

==Physics model==
As of version .5.04, in modeled the following features:

# Finite flame propagation rates and flame front acceleration and turbulence.
# Pressure drop across the disc orifice.
# Temperature increase in the unburned gases found within the chamber as pressure increases during propellant burning.
# Temperature/pressure decrease due to heat lost to the walls of the gun chamber and barrel.
# Performance differences due to different fuels (not complete as of this writing).
# Temperature effects on gas properties (and thus, performance).
# Performance limitations due to flow choking in the disc orifice or the barrel.
# Disc effective orifice increases due to lowered valve throat Mach number.
# Temperature (and thus pressure) drop in the barrel due to work performed by the gas accelerating the projectile.
# Gas leakage around the projectile in the barrel.
# Compressibility (Mach) effects on air pressure both in front of and behind the projectile to include the creation of shocks.

However, it does not consider:

#Energy losses associated with turbulence or frictional forces between the gas and the gun's chamber/barrel walls. In other words, pressure drops due to bends or rough edges in the gun's plumbing.
#Realistic combustion modeling.

As of right now, HGDT's accuracy when simulating hybrid cannons has not yet been thoroughly tested. Combustion simulations using atmospheric pressures have been matched with Burnt Latke's testing;
[http://thehalls-in-bfe.com/HGDT/Library/latkeL1.html Page 1]
[http://thehalls-in-bfe.com/HGDT/Library/latkeL3.html Page 2]

==Use==
See Hall's [http://www.thehalls-in-bfe.com/HGDT page] on use.

{{stub}}
[[category:Concepts]]

Co2

2010-12-23T17:30:44Z

Fnord: Redirected page to Carbon Dioxide

#REDIRECT [[Carbon Dioxide]]

Piston Valved Hybrid

2009-04-11T20:55:34Z

Fnord:

[this is under construction; currently nothing links here. I'll finish it eventually -fnord]

A '''piston-hybrid''' is a generic name for a [[hybrid]] that uses a valve other than a traditional [[burst disk]], the most common of which is a [[piston valve]]. However, like burst disk designs, they typically rely on the sudden increase in pressure upon ignition to actuate and work properly.

There are several advantages and disadvantages to this design:

'''Advantages'''

*Fast reset time
*No tools or burst disk material needed to reload
*Potential for semi/full auto firing

'''Disadvantages'''

*High mechanical stresses(large valves may require custom machining)
*Burst-pressure tuning is not always straightforward
*Typically higher weight

===Design Variations===

The easiest hybrid valve to construct is a traditional barrel-sealing piston valve, as it can be made from off-the-shelf fittings. Other options include [[snap valve|snap valves]], [[Toolies Piston Valve|toolies-style pistons]], and chamber-sealing valves. You should have a thorough understanding of pneumatic piston valves before attempting a hybrid valve.

==General Design Considerations==

Hybrid valves need to be built very tough in order to function safely. Materials such as steel, copper, brass and aluminum are preferred. [[PVC]] or other plastics are generally not acceptable or safe for such conditions.

Pistons need to be extremely impact resistant; pistons made from pvc or other brittle plastics may crack on the first use. Sealing face separation may also be an issue, so an ideal piston would be constructed entirely from [[neoprene]] rubber roundstock or similar materials.
If a heavy metal piston is used, a good [[bumper]] is necessary. A metal piston actuating can easily crack steel fittings if it gathers enough kinetic energy

If [[o-ring|o-rings]] are needed, seamless pipe and non-flammable grease should be used.

Safety [[safety valve|pop-off valves]] are commonly thought to be a necessity when constructing a hybrid valve. This is a MYTH, though they may be useful in certain designs.
A pop-off valve used as a safety device in a hybrid is useless, as the chamber should be able to contain your planned mix without sustaining damage.
Pop-offs can THEORETICALLY be used to cause a piston valve to open at a "lower than normal" pressure, but they have never been tested scientifically. They will also exhaust the air cushion that forms behind the piston, causing it to slam back harder.

==Building a Valve==

The type of valve you should choose depends on the type of gun you're constructing. Snap valves are good for small bores, pistons are good for general use, and toolie valves are good where compactness/low weight is necessary.

When you build a valve, it should be constructed with high opening pressure in mind. In a burst disk hybrid, opening pressure is increased by thickening the disk, but in a valved hybrid it is increased by adjusting the force holding the valve shut. Tuning your valve to open at the right pressure is critical to efficient operation, and is discussed (link)

It should also be noted that the d/4 rule does not necessarily apply to hybrids. In pneumatics, this rule is used to find how far a piston must move back for maximum flow through the barrel, with 1/4 of the barrel diameter being optimal. In a hybrid, air trapped behind the piston will resist backwards movement since there is nowhere for it to go. This may limit the travel of a d/4 compliant piston enough to cause significantly choked flow, as well as causing the valve to re-seal while pressure remains in the chamber. The easiest way to fix this problem is to increase the travel distance. A travel distance approximately equal to the porting diameter has been shown to work well.

==External links==

Opening Pressure

2009-04-03T14:54:42Z

Fnord: New page: Fnord's rambling on hybrid opening pressure. Currently under construction/no images. Opening pressure is a big concern you should have when constructing a valve. In a hybrid, you want th...

Fnord's rambling on hybrid opening pressure. Currently under construction/no images.

Opening pressure is a big concern you should have when constructing a valve. In a hybrid, you want the pressure to build until most of the fuel has burned, and then released at a near-peak pressure for the most power. In a burst disk design this is easily achieved by using thicker disks.
But how do you control what pressure a piston valve opens at?

The answer is simple, though it involves some math.
We'll start by looking at a barrel-sealer.

==Barrel Sealing Valves==
The easiest way to understand this is to think about what is keeping the valve shut, and what is trying to open it when ignition occurs. The diagram on the right shows how air pressure affects the valve.

As you can see, a valve with a large seat-diameter-to-piston-diameter ratio has more force holding it shut than a valve with a small barrel seat. The less 'red' area, the less force combustion can exert on the piston.
This is critical for a power-optimized hybrid, as ignition will cause the force pushing the piston back to rise fast, REALLY fast. A bad valve design will open at a pathetically low pressure and let large amounts of unburned fuel and air out the barrel.
A good rule for barrel-sealing valves is to use a seat diameter that is 80-90% of the piston diameter.

The equation for figuring out at what pressure your valve opens looks like this:

m * a / (p - a) + m = x

Where
m = mix pressure
a = valve seat OUTSIDE area
p = piston area

For example, here we can see what a valve using 1" and 1.5" sch40 steel will do at ~5x mix:

60 * 1.38 / (2 - 1.38) + 60 = ~193 psi absolute opening pressure.

When you build a valve, you should try to shoot for an opening pressure within 30-60% of the gun's peak pressure. Since 5x produces ~500 psi peak, this valve is good for hybrid use, and uses commonly available pipe dimensions.

You will most likely need a near-perfect seal around the piston when building a valve (a single floating o-ring is easy and ideal). This is because any pressure that leaks around the piston will raise its opening pressure, while decreasing the force available to open the valve. Too much leakage will cause the valve to remain shut, containing the explosion completely.

Also, keep in mind using a large seat will reduce flow if you extend it too far back into the valve (what the previous diagram shows is bad in this sense). In a good valve you'll be able to see the side of the piston when you look through the chamber port.

==Chamber Sealing Valves==

Chamber-sealers can also be used, though the rules governing opening pressure are reversed.
This means you want a smaller porting diameter, and a bigger piston diameter. The following equation will give you the opening pressure for a chamber sealer:

(p - a) * m / a + m = x

Where
m = mix pressure
a = valve seat INSIDE area (porting area)
p = piston area

Plugging in the numbers for 1" and 1.5" pipe gives a low opening pressure, while 1" and 2" pipe give good results.

(2 - .785) * 60 / .785 + 60 = ~152 psi
(3.14 - .785) * 60 / .785 + 60 = ~240 psi

As of writing this, no one has used a chamber sealing piston on a hybrid. They are more difficult because they require o-ring seals and seamless pipe to build. Carbon grit from repeated combustions may interfere with o-rings, so they should be cleaned occasionally.

==Snap valves==

These valves are ideal for small-bore hybrids, as they can be adjusted on the fly for any opening pressure. The only limiting factor is the spring compression.

Because they use a spring instead of air pressure, bore sizes over 1" diameter can be difficult to seal. A 1" porting valve disigned to open at 500 psi would require 392 pounds of spring closing force.

==Toolies-Style Piston Valves==

Toolie valves should follow the same rules as a barrel sealer, meaning the seat is 80-90% of the piston diameter.
However, in a toolie valve, the piston is the same diameter as the chamber. This means the sealing face will cut flow through the chamber down to almost 20%, when the port could normally handle about 65%.

The easiest way to remedy this is to cut the piston housing diameter with a bell reducer or reducing bushing, then scale the sealing face+porting down appropriately.

Toolie valves may be difficult to implement due to the fact that they occupy the chamber itself, reducing available space for fans and spark gaps.

==Diaphragm Valves==

Diaphragm valves have been used before and work roughly the same as piston valves, but off-the-shelf valves may run the risk of being damaged by high pressures.
When designing a valve, it is important to construct a pilot area that does not allow the diaphragm to stretch excessively when under ignition pressure. Backing the diaphragm with a metal plate for strength is advisable.

Equations for piston valves may not give accurate results for diaphragm valves, as flexing rubber behaves differently than a solid piston when under pressure.

Piston Valved Hybrid

2009-04-03T14:49:37Z

Fnord:

[this is under construction]

A '''piston-hybrid''' is a generic name for a [[hybrid]] that uses a valve other than a traditional [[burst disk]], the most common of which is a [[piston valve]]. However, like burst disk designs, they typically rely on the sudden increase in pressure upon ignition to actuate and work properly.

There are several advantages and disadvantages to this design:

'''Advantages'''

*Fast reset time
*No tools or burst disk material needed to reload
*Potential for semi/full auto firing

'''Disadvantages'''

*High mechanical stresses(large valves may require custom machining)
*Burst-pressure tuning is not always straightforward
*Typically higher weight

===Design Variations===

The easiest hybrid valve to construct is a traditional barrel-sealing piston valve, as it can be made from off-the-shelf fittings. Other options include [[snap valve|snap valves]], [[Toolies Piston Valve|toolies-style pistons]], and chamber-sealing valves. You should have a thorough understanding of pneumatic piston valves before attempting a hybrid valve.

==General Design Considerations==

Hybrid valves need to be built very tough in order to function safely. Materials such as steel, copper, brass and aluminum are preferred. [[PVC]] or other plastics are generally not acceptable or safe for such conditions.

Pistons need to be extremely impact resistant; pistons made from pvc or other brittle plastics may crack on the first use. Sealing face separation may also be an issue, so an ideal piston would be constructed entirely from [[neoprene]] rubber roundstock or similar materials.
If a heavy metal piston is used, a good [[bumper]] is necessary. A metal piston actuating can easily crack steel fittings if it gathers enough kinetic energy

If [[o-ring|o-rings]] are needed, seamless pipe and non-flammable grease should be used.

Safety [[safety valve|pop-off valves]] are commonly thought to be a necessity when constructing a hybrid valve. This is a MYTH, though they may be useful in certain designs.
A pop-off valve used as a safety device in a hybrid is useless, as the chamber should be able to contain your planned mix without sustaining damage.
Pop-offs can THEORETICALLY be used to cause a piston valve to open at a "lower than normal" pressure, but they have never been tested scientifically. They will also exhaust the air cushion that forms behind the piston, causing it to slam back harder.

==Building a Valve==

The type of valve you should choose depends on the type of gun you're constructing. Snap valves are good for small bores, pistons are good for general use, and toolie valves are good where compactness/low weight is necessary.

When you build a valve, it should be constructed with high opening pressure in mind. In a burst disk hybrid, opening pressure is increased by thickening the disk, but in a valved hybrid it is increased by adjusting the force holding the valve shut. Tuning your valve to open at the right pressure is critical to efficient operation, and is discussed (link)

It should also be noted that the d/4 rule does not necessarily apply to hybrids. In pneumatics, this rule is used to find how far a piston must move back for maximum flow through the barrel, with 1/4 of the barrel diameter being optimal. In a hybrid, air trapped behind the piston will resist backwards movement since there is nowhere for it to go. This may limit the travel of a d/4 compliant piston enough to cause significantly choked flow, as well as causing the valve to re-seal while pressure remains in the chamber. The easiest way to fix this problem is to increase the travel distance. A travel distance approximately equal to the porting diameter has been shown to work well.

==External links==

Piston Valved Hybrid

2009-04-03T14:41:18Z

Fnord: New page: [this is under construction] A '''piston-hybrid''' is a generic name for a hybrid that uses a valve other than a traditional burst disk, the most common of which is a [[piston val...

Hybrid cannon

2009-03-31T23:27:51Z

Fnord: bbq's are a legitimate option...

[[Image:hybrid.jpg|right|thumb|300px| A very well built hybrid, although it is not safe for handheld operation due to its use of a PVC chamber]]
A '''hybrid''' is a type of spudgun that combines principles of the [[combustion cannon|combustion]] and [[pneumatic cannon|pneumatic]] spudgun. It uses a pressurized mixture of [[fuel]] and air to get more power out of a given chamber volume than a normal combustion or pneumatic gun could.
The hybrid is capable of higher velocities than a combustion or pneumatic spudgun; projectiles fired by a hybrid have broken the sound barrier. This is possible because of the higher [[pressure]] and temperature gases generated by a hybrid [[combustion process|combustion]].

A hybrid launcher consists of seven basic elements:

*High pressure combustion [[chamber]]
*Pressure-triggered main [[valve]] (usually a [[burst disk]], see below)
*[[Barrel]]
*Fuel system (usually [[fuel meter|metered propane]])
*Air injection valve (usually [[schrader valve|schrader]] or [[quick disconnect|quick connect]])
*High-voltage [[Ignition source]]
*One or more [[pressure gauge]]s

==Operation theory==
A hybrid is first injected with a measured amount of fuel - much more than would be used in a regular combustion. However, without adequate oxygen, the mixture would be far too rich to ignite, so the chamber is then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a [[stoichiometric]] fuel/air ratio in the chamber.

A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, pressure gauges and fuel [[fuel meter|meters]] are used for this.

The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered [[ignition source]] such as a [[stungun]], [[flyback circuit]], or other high-voltage source; [[BBQ ignitor|grill igniters]] may be unreliable and require a very small [[spark gap]](typically 1mm or less) to work correctly in pressurized fuel/air environments.

The gases resulting from the combustion of the fuel/air mixture are released to the barrel via a self-operating valve of some sort, most commonly a [[burst disk]] because of it's simplicity and reliability, although self-venting [[piston valve|piston]]/[[diaphragm valve|diaphragm]] valves have been used. The valve is required to contain the pressure of the mixture pre-ignition, in other words, to prevent the pressurized fuel/air mixture from exiting out the barrel before ignition. Upon ignition of the fuel-air mix, the pressure rises and the valve opens.

===Safety===
A hybrid is one of the more dangerous types of launchers to build, apart from high pressure pneumatics. It is advised to only attempt to build one with pipe that can handle the high pressure environment (300+ [[Pressure gauge|PSI]]), generally SCH 40 steel or better. SCH 80 PVC has been used, but is not safe due to recurring fatiguing problems that have been observed in PVC hybrids and multiple failures even at low mixes. As with any launcher, the entire chamber is only rated to the spec of the lowest-rated part, so care must be taken when constructing the chamber of a hybrid. [[Remotely_activated_valve |Remote ignition]] is a must if PVC is used as a construction material, and is strongly advised for the initial testing of any hybrid. Although it was originally thought that mixes higher than 4x posed an unacceptable risk of [[DDT]] (deflagration to detonation transition), further calculations have revealed that the increased temperature of higher mixes barely counters the decreased burn rate cause by higher pre-ignition pressures, and that even a 20x mix will only burn a few m/s faster than a 1x mix. If DDT did occur, it would produce an extremely violent shock and pressure spike, which would cause any PVC chamber to shrapnel, and damage most steel or iron chambers beyond repair. The standard for hybrid construction is currently SCH 40 [[Steel Pipe|steel pipe]] and fittings, which have been tested in 2" sizes at mixes of up to 11x, repeatedly without failure. Theoretical burst pressure of SCH 40 2" steel pipe is >2kpsi, and no catastrophic failure has ever been achieved, accidentally or by design, in a hybrid made from safe materials.

Combustion cannon

2009-03-31T23:17:48Z

Fnord: minor stuff

[[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.

==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.

Main Page

2009-03-31T22:59:37Z

Fnord:

== 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.bavetta.com/aircannon.html Air Cannon Barrel Length Numerical Analysis]
*[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)]