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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: mopherman » Wed Jun 13, 2007 11:10 am

jackssmirkingrevenge wrote: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.


your not going to be able to searvice your piston thing? just going to cut it in half if something goes wrong?
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 13, 2007 11:46 am

that's the story with all my designs I'm afraid, if anything goes wrong inside I either cut it open or bin it. On the other hand, it dirves me to make designs that will be effectively maintenance free.
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Unread postAuthor: joannaardway » Wed Jun 13, 2007 11:49 am

Acdcmonkey1991 wrote: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...

Wikipedia is not a suitable legal resource, especially given that definitions change so much across the world.

It's usually fine as an encyclopedia - and that definition is fine for typical firearm explanation. But quote Wikipedia to the cops, and it won't cut it.

For accurate facts there, you'll have to use a government webpage, or one dedicated to firearms law in the correct country.

@JSR: I have to correct you on one point - a self contained cartridge is permitted in one situation.
Anything below 1 ft lb muzzle energy is not considered a firearm in the UK, so you can do absolutely anything below that limit, except stuff like exploding projectiles.

Not much good though - unless you intend on making a crazily complex airsoft gun.
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Unread postAuthor: A-98 » Wed Jun 13, 2007 11:56 am

once again, beautiful use of epoxy :D
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 13, 2007 12:02 pm

joannaardway wrote:@JSR: I have to correct you on one point - a self contained cartridge is permitted in one situation.
Anything below 1 ft lb muzzle energy is not considered a firearm in the UK, so you can do absolutely anything below that limit, except stuff like exploding projectiles.

Not much good though - unless you intend on making a crazily complex airsoft gun.


technically, there's no mention of power limits to the amendments in the law. Taken from the anti-social behaviour act 2003, the law bans the following:

any air rifle, air gun or air pistol which uses, or is designed or adapted for use with, a self-contained gas cartridge system


Of course the law isn't enforced for airsoft, for example airsoft 40mm grenades are effectively air cartridges and are sold openly in the UK.

It's a shame though, I had even seen a deactivated AK that had been converted to a straight-pull airgun using the Brocock cartridges. The ban was a typical government knee-jerk reaction in my opinion and hasn't done anything to reduce gun crime in Britain.
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Unread postAuthor: joannaardway » Wed Jun 13, 2007 12:27 pm

There may be no mention about the power in the most recent amendments, but the 1 ft lb point hasn't been removed since it was implemented.

Legally, 1 ft lb is defined as the minimum energy needed to pierce skin. So, anything below that isn't considered dangerous, so they let you do pretty much whatever.

Not that it's important, but it's at least nice to think that a vortex BBMG is completely legal, regardless of how quickly it fires.
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Unread postAuthor: Suppressive Fire » Wed Jun 13, 2007 2:50 pm

I think that was the thread jack. Even though its a combustion I herby quote Mr. Plow

My point is this: we travel a thin line that separates a spudgun from a firearm. The ATF letter that technically legalizes our hobby here in the US is not airtight. In fact, very few spudguns today actually meet the criteria specified in that letter for defining a potato cannon. By implementing characteristics of real firearms into our guns, how can we argue that they don't fall in the same catagory? IF you use cartridges, it is no longer a potato gun; same goes for using solid propellants. Picture yourself talking to a cop: how would you argue that your gun (which resembles an assault rifle) and uses contained cartridges is not a real gun? Sure, it isn't as powerful as a real firearm, and yes, it is made out of PVC, but I know I wouldn't want to be in that situation...

God forbid your cannon does get classified as a firearm... jailtime, anyone?
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 13, 2007 9:45 pm

joannaardway wrote:Not that it's important, but it's at least nice to think that a vortex BBMG is completely legal, regardless of how quickly it fires.


That depends on the efficiency of the design - full auto over 1 ft/lb is legally a section 5 weapon, ie banned for civillian ownership - and I've my ball-valve strafer at up around 320 fps with 8 grain 0.177 lead BBs, giving a muzzle energy of over 1.75 ft/lb per shot. My "conventional" vortex strafer with a 5mm barrel however could only manage about 0.8 ft/lbs with steel BBs if I recall correctly.
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Unread postAuthor: hi » Wed Jun 13, 2007 9:50 pm

i actually had a local cop fire my cannon and he said it was " pretty interesting".

this cop happens to be my friend's dad, so i think thats why he let it go.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: VH_man » Wed Jun 13, 2007 10:09 pm

i live right next to a cop....... hehe. he thinks my cannons are pretty cool. he just warns me not to shoot them at anyone and be safe and stuff and its all cool.........

in fact, he thought the strafer design was pretty ingenious.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 13, 2007 10:28 pm

fucksocks.

Just as I thought, I trimmed a little too much off the front of the piston, now its not sealing properly.

back to the drawing board :roll:
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Unread postAuthor: mopherman » Thu Jun 14, 2007 9:29 am

jack what kind of epoxie do you use for molding? whenever I mold stuff with 2 part, it comes out sticky and shitty looking.
do you lube the stuff up to get it to slide?
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 14, 2007 9:59 am

I use proper marine epoxy like this stuff, a bit more expensive to buy as it's in larger quantities but it will last you for many many projects.

I lube the sides of the tube with a thin coat of automotive grease and make sure all the surfaces are smooth so once the resin is dry, it pops out easily.
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Unread postAuthor: iknowmy3tables » Wed Jul 25, 2007 1:17 pm

dang I missed the heat of this thread but I just want to say that the main body of the cartridge should be bigger than the pipe used to hold the projectile, increasing C:B, and making it more like typical high velocity rifle rounds, and less like pistol rounds excluding the five-seven
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 26, 2007 1:10 am

This more of a mechanical interest project than one built for performance. I've had to to think while abroad, I have a few ideas I'd like to try out when I get home, watch this space.
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