My first working pengun- ammo questions...

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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SloppyJoeES
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Wed Dec 16, 2020 7:00 pm

I have finally completed a simple coaxial pengun, yet another copy of a copy of JSR's design from so long ago. I'm very happy with it!
20201216_154331_HDR.jpg
The build is made up of two 1/8" brass pipe nipples coupled together, with an OD 7mm ID 6mm stainless tube epoxied inside. Inside of that tube is the barrel, an OD 4mm ID 3mm stainless tube. The piston is a short section 6mm steel rod with a slice of 1/16" thick rubber epoxied to the top.
20201216_154401.jpg
This is my third attempt at one of these damn things, mostly owing to struggles getting a proper piston made. Concern that my piston would not work is why this one is built inside of pipe nipples- the valve can come off and the piston can be removed for service.
20201216_154425_HDR.jpg
The tube I ordered to be the barrel is supposedly 3mm, but 3mm steel ball bearings do not fit at all. Not even half of the bb will fit inside, so I am thinking it may be 2mm or perhaps 2.5mm. Any way to loosen the barrel, or should I just get new bearings? I would also love to hear other ideas for ammo.

Thanks for the guidance last year JSR. Took me damn near long enough to work it out though, what with school and everything else. The steel rod I eventually used as a piston was going to be a mandrel, to sharpen a piece of barrel cleanly enough that I could punch a proper piston out of rubber. Never could get one I was happy with.

I have been shooting it at 1000psi, but I might step up to 2000psi soon, once I receive some extremely high psi rated Schrader cores I ordered from an aviation supply
Last edited by SloppyJoeES on Wed Dec 16, 2020 8:01 pm, edited 1 time in total.
PracticallySane
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Wed Dec 16, 2020 7:13 pm

I have made a few pen guns, always thought shooting small nails was fun. Or "skewers" work as well.
I’m a scientist; because I invent, transform, create, and destroy for a living, and when I don’t like something about the world, I change it. ~Rick Sanchez.
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jackssmirkingrevenge
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Thu Dec 17, 2020 6:09 pm

Very cool!

interesting to see what performance will look like at high pressure.

I never really took them beyond 850 psi, maybe a tiny caliber 4500 psi pengun would be an interesting project...
Any way to loosen the barrel, or should I just get new bearings?
I would just get the right sized bearings, small nails with their heads cut off also work as PracticallySane suggested but only for very short ranges as they start to tumble.
hectmarr wrote:You have to make many weapons, because this field is long and short life
PracticallySane
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Thu Dec 17, 2020 6:28 pm

If you find some with the right size head, you dont need to remove it and it will apply some drag stability. I like the nails for hanging pictures.
I’m a scientist; because I invent, transform, create, and destroy for a living, and when I don’t like something about the world, I change it. ~Rick Sanchez.
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SloppyJoeES
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Thu Dec 17, 2020 7:39 pm

PracticallySane wrote:
Thu Dec 17, 2020 6:28 pm
If you find some with the right size head, you dont need to remove it and it will apply some drag stability. I like the nails for hanging pictures.
I found a couple nails around my apartment... I have also ordered more ball bearings and tiny tiny nails which should hopefully fit. I will try and remember to upload a video showing off this thing in action once I receive them. I predict pretty good performance at 1000psi. So far I have only used it to startle my girlfriend, for which it works very well :evil:

I disassembled it and took the piston out and I must say, I am glad I made this thing serviceable because the sealing face is already looking pretty rough. Let's see how long it goes before I must replace it...
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farcticox1
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Thu Dec 17, 2020 8:31 pm

Came to see a Penguin
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mrfoo
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Fri Dec 18, 2020 7:39 am

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SloppyJoeES
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Fri Dec 18, 2020 7:37 pm

20201218_163008.jpg
I shot a tin can with a nail using the pen gun @ 1000psi. I was quite happy with the results...

When I shot it, I saw orange sparks fly out, and it smelt like smoke... Is that normal?? Lol.

Entry:
20201218_162936.jpg
Exit:
20201218_162943.jpg
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farcticox1
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Fri Dec 18, 2020 8:31 pm

mrfoo wrote:
Fri Dec 18, 2020 7:39 am
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Cracking Gromit
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jackssmirkingrevenge
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Sat Dec 19, 2020 10:30 am

farcticox1 wrote:
Thu Dec 17, 2020 8:31 pm
Came to see a Penguin
That joke is literally as old as the first pen gun :roll: :D
SloppyJoeES wrote:
Fri Dec 18, 2020 7:37 pm
When I shot it, I saw orange sparks fly out, and it smelt like smoke... Is that normal?? Lol.
Hmmm... from the pen itself? Or the target?

Could it be that you had some lubricant in the barrel that ignited from the sudden compression?
hectmarr wrote:You have to make many weapons, because this field is long and short life
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hectmarr
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Sat Dec 19, 2020 10:51 am

I like it, and also, it is the perfect "weapon" to annihilate the state bureaucracy and its henchmen that take many hours from our ephemeral and interesting existence. You waste my time, and I pierce you! ;)
First the fact and then the law.
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SloppyJoeES
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Sat Dec 19, 2020 5:31 pm

jackssmirkingrevenge wrote:
Sat Dec 19, 2020 10:30 am
Hmmm... from the pen itself? Or the target?

Could it be that you had some lubricant in the barrel that ignited from the sudden compression?
It was from the target for sure. Maybe just from the steel hitting steel. I did lubricate the piston quite heavily with silicone grease, but I don't think that's flammable.

I have shot the same can a few more times since then and have not gotten the same sparks, which I find somewhat disappointing because I thought it was pretty cool.
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jackssmirkingrevenge
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Sat Dec 19, 2020 6:01 pm

Oh in that case, perfectly normal when punching through steel fast enough ;)

hectmarr wrote:You have to make many weapons, because this field is long and short life
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Anatine Duo
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Sun Dec 20, 2020 8:46 pm

looks fun... I really need to make one too
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hectmarr
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Tue Dec 22, 2020 9:14 pm

SloppyJoeES wrote:
Sat Dec 19, 2020 5:31 pm
jackssmirkingrevenge wrote:
Sat Dec 19, 2020 10:30 am
Hmmm... from the pen itself? Or the target?

Could it be that you had some lubricant in the barrel that ignited from the sudden compression?
It was from the target for sure. Maybe just from the steel hitting steel. I did lubricate the piston quite heavily with silicone grease, but I don't think that's flammable.

I have shot the same can a few more times since then and have not gotten the same sparks, which I find somewhat disappointing because I thought it was pretty cool.
If you want to get a bit of sparks and smoke, add a small drop of oil, like spring-loaded airguns do, with the dieseling effect. Your work was excellent, I'm thinking of building one like me too. :)
First the fact and then the law.
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