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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: Solar » Tue Jun 12, 2007 12:06 am

I have heard that it is illegal to place a spring loaded firing pin behind 40mm tubing in the U.S. . M203 airsoft clones get around this by using a levered pin that dislodges a springed mechanism inside the pre-charged cartridge.
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 12, 2007 1:59 am

Solar wrote:I have heard that it is illegal to place a spring loaded firing pin behind 40mm tubing in the U.S. . M203 airsoft clones get around this by using a levered pin that dislodges a springed mechanism inside the pre-charged cartridge.


Some thing like this:

Image

Are you sure?

NFA weapons are: machine guns, sound suppressors (a.k.a.
silencers), short barreled shotguns, short barreled rifles,
destructive devices and "any other weapons". Exactly what these
weapons are is defined in the law, as well as in court cases
interpreting the law. Withut going into to much detail, these are
what the categories encompass:

A machine gun is any gun that can fire more than one shot with
a single pull of the trigger, or a receiver of a machine gun, or a
combination of parts for assembling a machine gun, or a part or set
of parts for converting a gun into a machine gun.

A silencer is any device for muffling the gunshot of a portable
firearm, or any part or parts exclusively designed or intended for
such a device (see discussion below).

A short barreled shotgun is any shotgun (which is defined as a
shoulder fired, smooth bore firearm) with a barrel of less than 18"
or an overall length of less than 26", or any weapon made from a
shotgun falling into the same length parameters.

A short barreled rifle is a rifle (which is defined as a shoulder
fired, rifled bore firearm) with a barrel length of less than 16",
or an overall length of less than 26", or any weapon made from a
rifle falling into the same length parameters (like a pistol made
from a rifle). In measuring barrel length you do it from the
closed breech to the muzzle, see 27 CFR sec. 179.11. To measure
overall length do so along, "the distance between the extreme ends
of the weapon measured along a line parallel to the center line of
the bore." 27 CFR sec. 179.11. On a folding stock weapon you
measure with the stock extended, provided the stock is not readily
detachable, and the weapon is meant to be fired from the shoulder.

A destructive device (DD) can be two basic categories of things.
It can be an explosive, incendiary or poison gas weapon, like a
bomb or grenade. It can also be a firearm with a bore over 1/2",
with exceptions for sporting shotguns, among other things (see
discussion below). I call the second category large bore
destructive devices. As a general rule only this second category
is commercially available.

Any other weapons (AOW's) are a number of things; smooth bore
pistols, any pistol with more than one grip, (but see below) gadget
type guns (cane gun, pen gun) and shoulder fired weapons with both
rifled and smooth bore barrels between 12" and 18", that must be
manually reloaded (see discussion below).


It specifies firearms, no mention of air-powered weapons.
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Unread postAuthor: A-98 » Tue Jun 12, 2007 2:26 am

HA! so thats how those grenades work. ive always wondered. ive had all sorts of overly complicated ideas of my own, but thats relatively simple.
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 12, 2007 4:02 am

It's basically an inverse co-axial, with the barrels around the chamber, and instead of a pilot chamber holding the piston shut, it's held mechanically by the bearings.
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Unread postAuthor: Solar » Tue Jun 12, 2007 2:10 pm

I don't remember wher eI heard or read about the firing pin thing, but I am fairly certain that it is the case. I will look into it more.
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Unread postAuthor: Suppressive Fire » Tue Jun 12, 2007 3:04 pm

I said it was a fuzzy line. Not that it was illegal for sure. Just look into it because from what I just read you could push an argument either way on the subject. There was a thread on spudtech that quoted actual legislation I just wish I could find the stupid thing in the archive. You all may very well be right but there is no reason not to give the local police a call and see what they say.
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 12, 2007 9:16 pm

Suppressive Fire wrote:There was a thread on spudtech that quoted actual legislation I just wish I could find the stupid thing in the archive.


The only one I can think of is this one.
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Unread postAuthor: Acdcmonkey1991 » Tue Jun 12, 2007 9:26 pm

A firearm is a kinetic energy mechanical device that fires either a single or multiple projectiles propelled at high velocity by the gases produced by action of the rapid confined burning of a propellant.
-wikipedia

That basicly means that your design isn't considered a firearm. You still might wanna check with the cops though...
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 12, 2007 9:53 pm

or maybe not, why attract unnecessary attention to what I do in my free time in the privacy of my own home ;)
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Unread postAuthor: us sniper » Wed Jun 13, 2007 12:10 am

What about this design for your cartridge. To fill you push the push and fill the chamber with air. To get more power you just change the gas inside the cartridge.
http://i153.photobucket.com/albums/s240 ... tridge.jpg
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Unread postAuthor: A-98 » Wed Jun 13, 2007 12:25 am

that wont work as well, if at all. from what i see when you try to fill it it will just let the air out again, and theres no way for the air to get pas the "head" of the "piston". besides, saying that you fixed that, it wouldnt be as efficient as a piston.
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Last edited by A-98 on Wed Jun 13, 2007 11:53 am, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 13, 2007 1:30 am

us sniper wrote:What about this design for your cartridge. To fill you push the push and fill the chamber with air. To get more power you just change the gas inside the cartridge.
http://i153.photobucket.com/albums/s240 ... tridge.jpg


That is more or less how the Brocock Tandem Air Cartridge works, but as A-98 pointed out, given the lower pressures and larger calibres we're working with here, a piston design would be more efficient.

I cast the piston last night, photos to come when it's finished.
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Unread postAuthor: FreakyShotGlass » Wed Jun 13, 2007 2:16 am

For a prototype why don't you try and use the trigger mechanism from a cap gun. Would save time designing a trigger mech yourself (they can be really annoying to get right).
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 13, 2007 2:47 am

FreakyShotGlass wrote:For a prototype why don't you try and use the trigger mechanism from a cap gun. Would save time designing a trigger mech yourself (they can be really annoying to get right).


The idea is to do a basic check for performance by duct-taping the prototype cartridge to a barrel and seeing what sort of velocity I get, If it will put a parble through 1/4" thick plywood I'll be a happy bunny. If that works well, I'll cast a proper breech and see what sort of blowback energy is available and move from there.

I though about the cap-gun idea when making my mini-pistons, it would make a great compact single shot launcher.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 13, 2007 10:26 am

As per my original diagram here's the piston and cartridge body, all that I need to do is cap the back end with epoxy and a schrader valve.

Note that I cut down the sides of the front portion of the piston to allow air to flow out on firing. Also note the back of the cartridge body has been roughened to facilitate the adhesion of the epoxy.
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Attachments
pccpistonside.jpg
side view
pccpistonside.jpg (31.73 KiB) Viewed 2734 times
pccpistonfront.jpg
front view
pccpistonfront.jpg (35.11 KiB) Viewed 2734 times
pccpistonback.jpg
back view
pccpistonback.jpg (35.62 KiB) Viewed 2734 times
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