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burst disk cartridge idea

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: Infernal Maveric » Fri Sep 21, 2007 10:49 am

The BB will need to be forced into the holding section (AKA Perfect Fit), otherwise, as the pressure would be equal on both sides of the BB, Meaning it could roll about in the chamber.
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Unread postAuthor: williamfeldmann » Fri Sep 21, 2007 11:29 am

I assume the drawings you made are somewhat to scale.

Where are you going to find a spring that will move the bolt hard enough to hit the cartridge forward and be light enough to be pushed back into the locked position? In real semiauto firearms with gas blowback (basically what your design is) the spring is extremely lightweight. The firing pin strikes the primer with less energy than you can create with a rubberband. That spring doesn't have to "move" anything, yours would thus increasing the necessary strength.

I only ask because if the pics are at all to scale we are dealing with some distance of play on that cartridge.
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Unread postAuthor: Hubb » Fri Sep 21, 2007 11:34 am

I was just thinking about what maveric said. Maybe you could place the bb on the other side of the bust disc with some kind of detent to keep it from moving until you wanted it to.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 21, 2007 12:05 pm

Where are you going to find a spring that will move the bolt hard enough to hit the cartridge forward and be light enough to be pushed back into the locked position? In real semiauto firearms with gas blowback (basically what your design is) the spring is extremely lightweight. The firing pin strikes the primer with less energy than you can create with a rubberband. That spring doesn't have to "move" anything, yours would thus increasing the necessary strength.


It's not just the firing pin that the psring has to move - in a direct blowback submachinegun, the spring also has to shift a very heavy bolt, take this Sten for example:

Image

The bolt isn't locked in place and the cartridge tries to move back with considerable force, so a heavy bolt and strong spring are needed to resist the motion, certainly stronger than a rubber band.

You're right though, as I pointed out earlier, the major difficulty with this project lies with some unknown factors - mostly a) how much energy is needed to move the cartridge and burst the disk and b) how much energy does the cartridge move back with.

If a) is greater then b) then it cannot be semi/full auto without external help. Still, only one way to find out, I'm drawing up plans for an attachment to be machined so I can run some tests.
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Unread postAuthor: williamfeldmann » Fri Sep 21, 2007 12:33 pm

My bad, I totally forgot about the bolt, I was thinking the firing mechanism, I'll go find a cliff after I finish :)

What about a second air chamber behind the bolt.

Use the bolt like a piston in a piston gun just with no sealing face. The air pressure behind the bolt can shove the bolt forward when released hitting the cartridge forward and releasing the air behind the bolt as it clears some release port or the action itself.

The barrel punctures the cartidge and fires, shoving the bolt back, with nothing resisting it now, ideally back over the trigger mechanism that will hold it in place during the loading and charging process.

If you use something very similar to a trigger and seer mechanism (i think you designed one for firing a type of piston) you should be able to release the bolt whenever, at any pressure as long as it is enough to move the bolt. The small chamber behind the bolt doesn't have to be big, only big enough to shove the bolt a couple of inches until the pressure is released. You could ideally run it off of a paintball tank and regulator since the volume isn't that big and with preloaded cartridges you could have quite a few shots off that system.
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Unread postAuthor: FeLeX » Fri Sep 21, 2007 4:58 pm

You can sharpen certain parts of the pipe that bursts the disk and use a very light spring. If you don't understand what I am talking about the tell me and Ill draw up a diagram.
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 22, 2007 1:16 am

Use the bolt like a piston in a piston gun just with no sealing face. The air pressure behind the bolt can shove the bolt forward when released hitting the cartridge forward and releasing the air behind the bolt as it clears some release port or the action itself.


That would work but it's a little too complex for my liking, I had made a self contained air piston during my combustion cartridge testing and even that was a little over the top, I'd really like to keep things as basic as possible.

I'm hoping the cartridge will have more "blowback" power than my previous attempt at a preloaded pneumatic cartridge, for several reasons - in comparison, there's less dead space, a much more efficient valve and more importantly, since the calibre is reduced to 6mm, the high pressure in the breech will reduce at a much slower rate.

You can sharpen certain parts of the pipe that bursts the disk and use a very light spring.


Bursting the disk is just one of the spring's jobs, it also has to pick up a relatively heavy cartridge overcoming the drag of a spring loaded magazine. Next step is to make a prototype cartridge and breech and see exactly what sort of force it needs to burst and what sort of kick the cart has.
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Unread postAuthor: Novacastrian » Sat Sep 22, 2007 1:59 am

You need someone with a cnc JSR.
Pump them out by the hundred! :twisted:
The price you will pay for manual machining would be comparitive to automated machining- and you get more units, of course there is material costs...
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 22, 2007 2:19 am

I'd like to make sure it works before ordering them in their thousands ;) I'm not settled on the final design though, I'm looking at this idea again.
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Unread postAuthor: williamfeldmann » Sat Sep 22, 2007 8:34 am

Making the distance that the catridge moves will minimize the blowback force necessary. Your only problem will be getting the BB out of the gun before the cartridge get far enough back to release all its pressure.

The gun will not work at peak effeceincy but that is the nature of the system you are building.
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Unread postAuthor: FeLeX » Sun Sep 23, 2007 3:22 pm

Are you trying to make a semi auto gun? If not then just make a rifle with a bolt. Every time you cock it the empty cartridge will be ejected. Or make a double barrel shotty.
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Unread postAuthor: Modderxtrordanare » Sun Sep 23, 2007 5:39 pm

Are you trying to make a semi auto gun? If not then just make a rifle with a bolt. Every time you cock it the empty cartridge will be ejected. Or make a double barrel shotty.


Can you not read the thread?
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Unread postAuthor: FeLeX » Sun Sep 23, 2007 9:01 pm

Can you go dip your smart a$$ in acid? I was just wondering if it is very important to him that the gun is semi auto. Chill the heck out.
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 23, 2007 11:14 pm

FeLeX wrote:Are you trying to make a semi auto gun? If not then just make a rifle with a bolt. Every time you cock it the empty cartridge will be ejected. Or make a double barrel shotty.


I've made pneumatic and combustion catridges that worked well as far as firing was concerned, but without the necessary cojones to eject and reload another cartridge, which is what I'm aiming for.

The above idea has been put on hold while I play with rotating breeches :)
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Unread postAuthor: FeLeX » Mon Sep 24, 2007 8:22 pm

Hmm I think since burst disk is such raw power it might work. But then again could those brocock (or how ever you spell) air cartridges cycle? I think its the whole pressure spike.
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