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preloaded pneumatic cartridge

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: pyrogeek » Thu Jul 26, 2007 1:27 am

The cartridge idea is interesting. But having semi auto is already hard enough. And once you get the cycling action done to cycle a new round in, you could just have it cycle a new projectile in and have it open a smaller chamber that would charge from a larger higher pressure one. Maybe some sort of long bolt that would simultaneously chamber a new round and open a valve that would allow the small chamber to fill.
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 26, 2007 1:34 am

Interesting thoughts but the idea here is to have the cartridge as a completely self contained unit carrying the projectile and air necessary to fire - this complicates cartridge construction slightly but overall I think it would be the simplest system.

Even if it doesn't have enough energy to eject and cycle a new cartridge, this could be done manually and would still make a worthwhile effort.
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Unread postAuthor: iknowmy3tables » Thu Jul 26, 2007 10:02 am

well soo... what methods or precauions have you taken to ensure that the cartridges come out identical like any pre made parts or fabrication methods cause I know I would have trouble epoxy casting all the parts identically,
also this is a bolt action right? but just what loading and ejection system are you planing
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 27, 2007 3:32 am

Really the only parameters that have to be identical are the length and the position of the schrader, otherwise internally you can have some variations as long as it works.

I was thinking more straight-pull than bolt action, the hope is that the cartridges will eject themselves, though maybe I'll have to use an assault rifle style bolt to chamber a new one, we'll see. Version 2.0 should look something like my 6mm mini-piston designs with the barrel cut off.
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Unread postAuthor: Hawkeye » Fri Jul 27, 2007 9:02 am

Jack, I have made a fill valve which is like a large schrader. It is a brass reducer that is 1/4 on one side and an 1/8 on the other. The inner lip where the transition in size occurs provides the face for the small o-ring(on a metal spindle) to seal against.
Using a larger fill valve makes it easier to have a more substantial "firing pin" that will exhaust faster. On the other hand you need to make a pump that threads onto the 1/8th side of the fill valve. Not very hard to do and you can fill your cartridges a good deal faster than with a shock pump.
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 29, 2007 12:06 am

I was contemplatng making my own valves - not for performance, rather to make the whole setup more "cartridgy" - but given the tiny pilot volume in this case (what I'm planning - 1/2 inch piston chamber with 1/8 inch piston movement - jyst like my 6mm minis - a schrader is more than adequate, for now I'm willing to live with it.
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Unread postAuthor: Hubb » Sun Jul 29, 2007 2:33 am

This is a very interesting concept and I look forward to seeing a working model.

I know I am a little late on the matter but I figured I would clear this whole "classified as a firearm" thing up.

In the United States, under title 18, section 921:
(a)(3)a firearm is defined as
(A) any weapon (including a starter gun) which will or is designed to or may readily be converted to expel a projectile by the action of an explosive;
(D) any destructive device.
(4) The term “destructive device” means—
blah, blah, blah
(B) any type of weapon...by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, and which has any barrel with a bore of more than one-half inch in diameter; and
(C) any combination of parts either designed or intended for use in converting any device into any destructive device described in subparagraph (A) or (B) and from which a destructive device may be readily assembled.
The term “destructive device”shall not include any device which is neither designed nor redesigned for use as a weapon;...or any other device which the Attorney General finds is not likely to be used as a weapon, is an antique, or is a rifle which the owner intends to use solely for sporting, recreational or cultural purposes.

All that above basically states that as long as a devise is used for sporting or recreational purposes, it is not classified as a firearm or destructive devise, but I'm sure you already knew that.

And this is how it relates to this subject:
(17)
(A) The term “ammunition” means ammunition or cartridge cases, primers, bullets, or propellant powder DESIGNED FOR USE IN A FIREARM.

In short, your cartridge is not classified as ammunition due to the fact that it is not used in a firearm, and, therefore, is not classified as "illegal", at least in the US anyways. As far as any other countries, I'm not sure how their laws are, but I'm sure they are similar.
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Unread postAuthor: Modderxtrordanare » Sun Jul 29, 2007 5:19 am

Edit.
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Last edited by Modderxtrordanare on Sun Jul 29, 2007 3:10 pm, edited 1 time in total.
Spudding since '05. Proud waster of plumbing and plumbing accessories.

-Wiki
-How-To: Modding a Sprinkler Valve
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 29, 2007 6:10 am

It's all a question of how you use it really. No one's going to send you to jail for launching a few spuds in your own back yard, or search your room for suspciously put together PVC pipes, but if you're going to make holes in your neighbour's car windows, you can expect trouble whatever you use.
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Unread postAuthor: VH_man » Sun Jul 29, 2007 7:28 am

haha. thats exactly how i explain to my friends that i wont get arrested.

"if im being an idiot and running around the block shooting peoples cats, does the fuzz have a problem that i have a tater gun? yes, very much so. if im just shooting cans in my backyard? they wanna have a shot......"
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 30, 2007 11:11 am

I made a small experiment today to gauge the potential power, wrapped tape around the muzzle of one of my mini piston designs and stuffed it into a 2 foot length of 17mm pipe. at 300 psi it put a marble clean through a sheet of 1/4" ply, pretty decent - now the idea is to have a cartridhe that is practically identical to the above launcher, but with the barrel chopped off to become a port. Will start construction as soon as I'm done making up for lost time with the better half :)
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Unread postAuthor: Acdcmonkey1991 » Mon Jul 30, 2007 3:24 pm

I cant wait for you to finish it, it sounds awesome.
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VH was awesome!!
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Unread postAuthor: zomgwtfbbq » Thu Aug 02, 2007 1:04 pm

I am building a similar spud gun to yours, except the air reservoir will be in the gun and it will have a small bore, hence I will be using a sprinkler valve instead. I wish you all the best! Mazel tov!
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Unread postAuthor: zomgwtfbbq » Thu Aug 02, 2007 2:29 pm

This is the diagram of my spud gun. It is still in its early stages. The problem I have here is that the bolt is too long and ugly.
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Unread postAuthor: Skywalker » Sun Aug 05, 2007 8:42 pm

This sounds like a better idea than your previous cartridge pneumatic! I always like to see what Jack comes up with; you seem to have some of the more creative ideas around here.

Is flow going to be a problem with the cartridges? Your cartridge barrel is necessarily going to be a great deal smaller than your actual barrel, otherwise you wouldn't have much chamber volume, and would have more dead space instead. But I guess if you are working with insanely high pressure it won't be a huge deal.

Could you make a 'magnum' cartridge, so that your ammo actually goes into the cartridge barrel? The end result would be like a coaxial gun with one barrel and exchangeable chambers. I guess that wouldn't make too much sense, though: may as well have a barrel for each chamber.
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