fl(air) gun - mechanically locked pneumatic cartridge for a 26.5mm flare gun

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
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jackssmirkingrevenge
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Wed Jan 18, 2023 9:40 am

I thought this deserved a separate thread from the earlier development.

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Cartridge with a Polish flare gun from the 1950s based on the Soviet SPSh-44.

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Cartridge disassembled, most parts are machined from 12L14 steel apart from the body that is 6061 aluminum



Operating principle roughly to scale. The effective area of the piston is just 0.157 square centimeters or 0.024 square inches, but at 3000 psi that's a force of 72 lbs on the ball locks, in hindsight that difference in diameter could have been smaller.

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Cartridge inserted in the launcher



Video with a more detailed explanation of the mechanism and some action shots

Image

Test slugs made from 12 g CO2 capsules, the top two have small screws inserted in the nose and lead filling on the inside.

From top to bottom here are the weights and measured velocities and muzzle energy:

19.8g - 277 fps - 52 ft lbs

13.0g - 401 fps - 72 ft lbs

7.9g - 486 fps - 64 ft lbs

Normally more projectile weight gives more energy, but a dynamic at play here is that the projectile tail being hollow means there is more "dead" volume in the barrel, giving the air more space to expand and therefore dropping pressure.

Image

Aluminum dart with a steel core, weight is 20.7 grams but I didn't measure the velocity, presumably it's below 300 fps.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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mobile chernobyl
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Wed Jan 18, 2023 3:12 pm

This is amazing. I love all the effort to keep it looking stock and completely reversable if desiring to use a conventional flare. The use of the CO2 powerlet sections as ammo is also very clever in a world of expensive ammo. I've utilized them in the past on builds and it was fun shooting full ones into hard targets.

I log back into this site every month to see what's new. This really has me wanting to get a lathe again!

Great work as always!
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ToasT
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Tue Jan 24, 2023 2:35 am

Really nice work, I initially thought I was looking at an actual pneumatic flare gun by its original design, and thought that is cool.

I really shouldn't have considering it was made by you haha.

I love the conversion idea, and effort in keeping it looking stock. Nice valve design too, I cant say I have seen one working like that before.
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jackssmirkingrevenge
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Fri Feb 03, 2023 10:57 am

Thank you gents!
mobile chernobyl wrote:
Wed Jan 18, 2023 3:12 pm
I love all the effort to keep it looking stock and completely reversable if desiring to use a conventional flare.
It also means that the cartridge can be used in any 26.5mm flare gun, I'm really tempted to make a 12 gauge version.
I log back into this site every month to see what's new. This really has me wanting to get a lathe again!


The house would feel empty without one :D
I cant say I have seen one working like that before
The basic principle is the same as used in 40mm grenades for airsoft:

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hectmarr wrote:You have to make many weapons, because this field is long and short life
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SubsonicSpud
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Wed Nov 08, 2023 2:29 am

jackssmirkingrevenge wrote:
Wed Jan 18, 2023 9:40 am
I thought this deserved a separate thread from the earlier development.

Image

Cartridge with a Polish flare gun from the 1950s based on the Soviet SPSh-44.

Image

Cartridge disassembled, most parts are machined from 12L14 steel apart from the body that is 6061 aluminum



Operating principle roughly to scale. The effective area of the piston is just 0.157 square centimeters or 0.024 square inches, but at 3000 psi that's a force of 72 lbs on the ball locks, in hindsight that difference in diameter could have been smaller.

Image

Cartridge inserted in the launcher



Video with a more detailed explanation of the mechanism and some action shots

Image

Test slugs made from 12 g CO2 capsules, the top two have small screws inserted in the nose and lead filling on the inside.

From top to bottom here are the weights and measured velocities and muzzle energy:

19.8g - 277 fps - 52 ft lbs

13.0g - 401 fps - 72 ft lbs

7.9g - 486 fps - 64 ft lbs

Normally more projectile weight gives more energy, but a dynamic at play here is that the projectile tail being hollow means there is more "dead" volume in the barrel, giving the air more space to expand and therefore dropping pressure.

Image

Aluminum dart with a steel core, weight is 20.7 grams but I didn't measure the velocity, presumably it's below 300 fps.
Mate, that’s cool stuff, I miss the days of air gun fabrication 10-15years ago. Its awesome to see you got more equipment to work with now, working with epoxy would have been tedious.
Any other stand out builds or ideas on here over the last 10years I’ve been absent?
My holy grail would still be a large caliber cartridge ejecting semi auto. I should complete that QEV repeater build one day.
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Wed Nov 08, 2023 6:46 am

SubsonicSpud wrote:
Wed Nov 08, 2023 2:29 am
Any other stand out builds or ideas on here over the last 10years I’ve been absent?
My holy grail would still be a large caliber cartridge ejecting semi auto. I should complete that QEV repeater build one day.
There's been a lot of small and intricate hybrid builds especially by hectmarr. But ten years? I remember back in 2013 we were seeing some neat piston hybrids or maybe that was a little earlier. ;)
You should get on that QEV repeater, what once cost $200 from places like McMaster or fastenal you can pick up for $20 on Amazon these days.
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jackssmirkingrevenge
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Thu Nov 09, 2023 10:49 am

SubsonicSpud wrote:
Wed Nov 08, 2023 2:29 am
Mate, that’s cool stuff, I miss the days of air gun fabrication 10-15years ago.
The online landscape has changed, social media has effectively killed off this kind of forum for many such hobbies, and the majority of the cadre that was keeping Spudfiles alive has grown up or moved on and there haven't been new generations to fill that gap. It's unfortunate but that's progress I suppose :roll:
Any other stand out builds or ideas on here over the last 10years I’ve been absent?
As mark.f mentioned the outstanding projects recently have been by one distinguished Argentinian gentleman, it's a shame that there isn't the same audience out there to appreciate it.

These days I personally seem to do more "restomodding" of air guns like this or this but I have dabbled a little with hybrids recently, more to come soon :)
hectmarr wrote:You have to make many weapons, because this field is long and short life
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SubsonicSpud
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Fri Nov 10, 2023 4:46 am

jackssmirkingrevenge wrote:
Thu Nov 09, 2023 10:49 am
SubsonicSpud wrote:
Wed Nov 08, 2023 2:29 am
Mate, that’s cool stuff, I miss the days of air gun fabrication 10-15years ago.
The online landscape has changed, social media has effectively killed off this kind of forum for many such hobbies, and the majority of the cadre that was keeping Spudfiles alive has grown up or moved on and there haven't been new generations to fill that gap. It's unfortunate but that's progress I suppose :roll:
Any other stand out builds or ideas on here over the last 10years I’ve been absent?
As mark.f mentioned the outstanding projects recently have been by one distinguished Argentinian gentleman, it's a shame that there isn't the same audience out there to appreciate it.

These days I personally seem to do more "restomodding" of air guns like this or this but I have dabbled a little with hybrids recently, more to come soon :)
Those hybrid builds are impressive.

100% right about forums dying, I’ve noticed on many other forums as well. It’s a shame because Facebook groups are not great for archive or search purposes.

Perhaps we need to have a SpudFiles group as well 😆
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jackssmirkingrevenge
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Thu Dec 14, 2023 11:54 am

While using a single o-ring as both a seat seal and a check valve for filling functioned as a concept, I noticed that sometimes while purging the air line it would not reseal immediately, resulting in lower pressure in the cartridge and inconsistent performance, so I've modified the design with a separate oversized o-ring in a ported groove. This allows air to leak past it when coming from the line but seals in the groove when like line is purged, and so far it seals well. Here is a diagram comparing the first iteration on top and the modified design at the bottom:

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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Fri Dec 15, 2023 2:56 pm

jackssmirkingrevenge wrote:
Thu Dec 14, 2023 11:54 am
While using a single o-ring as both a seat seal and a check valve for filling functioned as a concept, I noticed that sometimes while purging the air line it would not reseal immediately, resulting in lower pressure in the cartridge and inconsistent performance, so I've modified the design with a separate oversized o-ring in a ported groove. This allows air to leak past it when coming from the line but seals in the groove when like line is purged, and so far it seals well. Here is a diagram comparing the first iteration on top and the modified design at the bottom:

Image
I like the solution you used and I take note of it for my existential problems with homemade hybrid weapons! It's pretty simple to do and, from what you say, it works well. Interesting!! :)
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Fri Dec 15, 2023 3:12 pm

This modification idea could be used as an easy-to-manufacture check valve. The important thing is that it seals quickly without any spring.
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jackssmirkingrevenge
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Sat Dec 16, 2023 11:28 am

Here are some details of the valve, first with o-ring in place and then slide down to show the groove:

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Also interesting to note the about of wear happening the two areas where the locking balls contact, on the firing pin as well as the inner edge of the piston:

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It doesn't impede function yet but clearly when working with thousands of psi of pressure a harder steel would be a more durable choice of material.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Sat Dec 16, 2023 12:10 pm

Awesome!! You're right, with steel it will last longer... I never thought that the abuse would be so much, but after seeing aluminum, they are very harsh operating conditions. Nice pictures!! :)
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Tue Dec 19, 2023 10:35 am

I agree with Hectmarr that is a neat way to build a check valve.
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