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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: jackssmirkingrevenge » Sun Aug 05, 2007 9:07 pm

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.


That would be ideal in terms of power, but personally there are two disadvantages, first of all since I don't have the benefit of a lathe, getting the cart to line up 100% with the breech would be very difficult. Secondly, the cartridge would be too bulky, for example for a 0.75" (19.05mm) barrel I'd like to have a cartridge that's dimensionally close to a 20mm cannon round, but as a co-axial it would be more like the size of a 40mm round.
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Unread postAuthor: zomgwtfbbq » Mon Aug 06, 2007 9:50 am

Jack, when will you post more new photos? :D
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Unread postAuthor: jackssmirkingrevenge » Mon Aug 06, 2007 10:04 am

when I actually shift my posterior and get to work - still trying to work out the best caliber and configuration, I'm torn between self contained cartridges or a re-visit of the cartridge fed concept, decisions decisions - and in the mean time going through Medal of Honor - Pacific Assault all in the name of "research" :D
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Unread postAuthor: zomgwtfbbq » Mon Aug 06, 2007 11:06 am

Ha ha ha. All the best to you man. I will be heading down to the arts and craft shop tomorrow to look for some of my parts. Ha ha this is probably the only form of shopping I do.
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Unread postAuthor: jackssmirkingrevenge » Mon Aug 06, 2007 11:59 am

zomgwtfbbq wrote:Ha ha this is probably the only form of shopping I do.


Enjoy it while you can, my g/f decided my wardrobe was still that of a teenager (hey, I was comfortable) and in the past week I've spent almost $600 on shirts, pants and shoes :(
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 08, 2007 2:33 am

Finally made some progress, started making cartridge version 2.0 :D
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P1010011.JPG
Basic components - the "barrel" (actually an air duct) with rubber tubing added epoxied in place (with the epoxy smoothed down to streamlined shape in my "lathe" - a drill clamped in a vice :D ), the epoxy piston (now sanded down to give a smooth face), syringe tubing (which still has to be cut down) and cut down schrader valve. Next to the PVC body is a genuine WW2 20mm cartridge for scale, the actual caliber of the launcher will be 19mm
P1010009.JPG
The cured piston pops out easily, especially with some light lubing of the syringe tube.
P1010007.JPG
Some insight into how I make my pistons - in this case, I simply cut off the nozzle face of a 5mL syringe and poured the epoxy in.
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Unread postAuthor: wannabie » Wed Aug 08, 2007 2:53 am

I get it :P i was staring at that last picture for about 5 minutes untill i realised how it worked :lol: i need to sleep...

that piston looks really tight what type of epoxy do you use?
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In epoxy we trust.
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 08, 2007 4:22 am

wannabie wrote:that piston looks really tight what type of epoxy do you use?


Of course it's tight, it's exactly the same diameter as the tube it will be housed in, because it was after all cast in it :wink:

Re: the epoxy type, see page 4 of this thread.
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Unread postAuthor: joannaardway » Wed Aug 08, 2007 10:57 am

Very nice. Kudos for the excellent work.

I'm seriously tempted to try this myself now - sod the legality.
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 08, 2007 2:44 pm

joannaardway wrote:Very nice. Kudos for the excellent work.


Cheers :)

Well, the cart is basically ready. The epoxy's still curing, I know I shouldn't have but I did a very quick test at low pressure and woo! it worked :D (It's always a bit hit-and-miss when you're dealing with epoxy, you know that if it doesnt work then you're screwed and have to start over) - next step is to duct tape it to a barrel and evaluate the performance (and make a few vidoes, as it is i think it's the most compact 3/4" launcher ever :D ), if I consider it to be worthwhile - my current standard is making a 3/4" hole through 1/4" ply - then I'll move on to building that anti-material rifle I always wanted :D

Anyways, on to the pictures:
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Attachments
cartridgev2comparison.jpg
As a matter of interest, here's how it compares to some firearm cartridges, from left to right: 22LR, 9mm pistol, 7.62mm Russian, 5.56mm NATO, 7.62mm NATO, 0.303 British and 20mm cannon
cartridgev2base.jpg
cartridge base - note how in this design the cartridge is recessed (I can still fill it with my shock pump because the pipe screws on to the schrader) to protect the schrader from damage when the cartridge is ejected
cartridgev2front.jpg
cartridge front, where the projectile will sit
cartridgev2diagram.JPG
internal diagram
cartridgev2diagram.JPG (31.5 KiB) Viewed 1058 times
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Unread postAuthor: Skywalker » Wed Aug 08, 2007 2:51 pm

Woot! Looks slick! I can't wait to see how the test fires go. How many will you make if it works? A dozen or so?

Are you going to just let the ejected carts fall to the ground? I guess that will work, b/c they should be easier to find than those little brass thingys you had on your earlier cart system. And I suppose it defeats the purpose of having carts if they don't eject, right?
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 08, 2007 2:59 pm

The whole point of this project is to see the carts fly out, of course I'm going to let them eject :D assuming they have enough power to eject themselves of course, it's a pretty heavy thing and that remains to be seen. I'm thinking it will probably be like my other system in that it will need a bolt stop to chamber another cart. Ah well, we'll see. I guess I'll make around 5 in all. The Lahti L39 which should form the basis for my launcher had a 10 round mag, but then again, I don't have to face soviet tanks either :)
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Unread postAuthor: frankrede » Wed Aug 08, 2007 3:10 pm

jackssmirkingrevenge wrote:The whole point of this project is to see the carts fly out, of course I'm going to let them eject :D assuming they have enough power to eject themselves of course, it's a pretty heavy thing and that remains to be seen. I'm thinking it will probably be like my other system in that it will need a bolt stop to chamber another cart. Ah well, we'll see. I guess I'll make around 5 in all. The Lahti L39 which should form the basis for my launcher had a 10 round mag, but then again, I don't have to face soviet tanks either :)
I don't have to face soviet tanks *yet*
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 08, 2007 3:16 pm

frankrede wrote:I don't have to face soviet tanks *yet*


Even with its 50,000 ft/lbs, the Lahti was relatively useless against WW2 tanks, I doubt a PVC replica will be of much use against what the modern Russian armament industry has to offer.
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Unread postAuthor: Hawkeye » Wed Aug 08, 2007 3:54 pm

I think it would work better if it was shorter with a long piston to eliminate all that dead volume in the slim inner tube. Wasn't that your original plan?
3/4 inch copper and various fittings makes a perfect marble shell.
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