12 bore HPA coaxial

[jackssmirkingrevenge]

Edit 12/07/2010:

Integral suppressor disguised as magazine/pump added:



Suppressor internal configuration and planned trigger/pistol grip configuration:



Fed up of playing with countless 1mm BBMG prototypes, I figured I'd take a break and play with something a little bigger

I've been wanting to build something like this ever since I got my first paintball tank. Nothing exceptional about the design, made with my usual epoxy endcap/piston construction as the internal diagram shows. Barrel is 18 inches of 0.75" PVC. The plan is to take it to 800 psi, so far I've only taken it to 500 psi. A quick chrony test showed a healthy 192 fps for a 30 gram empty CO₂ capsule, just under 38 ft/lbs of muzzle energy. Pretty damn loud too, I might be persuaded to fit it with a pistol grip and a suppresser styled like a shotgun pump.

Some obligatory high speed footage, Here it is at 500 psi firing a CO₂ capsule at an old PC mouse shell, and a section of 1/4" fibreboard.

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Soup tin at 500 psi:

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Some earlier tests at 100 psi, the capsule was only doing around 40 fps:

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edit: Here's an round made with the opposite side for "armour piercing" effect, due to very poor sectional density it didn't go all the way through but made a nice enough hole in the 1mm steel sheet. A saboted dart would have gone through several sheets like butter, and I still have yet to turn it up to 800 psi...

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No problems with a pellet tin lid and the 1/4" fibreboard behind it though:

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edit: this project is now defunct but the barrel is still in use grafted to a hybrid chamber

[chinnerz]

haha nice hand canon!!
I cant wait to see the finished product with pistol grip

[jackssmirkingrevenge]

Here's how it might looks like if I bother with a pistol grip and suppressor:

[POLAND_SPUD]

nice but it should be valveless and full auto

[c11man]

very nice and with decent power, i would have used a bigger chamber but thats just me

[jackssmirkingrevenge]

nice but it should be valveless and full auto

It actually felt slightly weird making a single shot piston valve

I would have used a bigger chamber but thats just me

It's loud enough as it is

[spudamine]

how high a pressure will you trust that PVC barrel to? I'm sure somebody posted a coax where the chamber pressure has crushed the barrel from the outside I'd try and dig up the thread but I suspect you could find it a lot faster than me

[jackssmirkingrevenge]

This stuff was a wall thickness of 3.5mm and I've been quite happy to take it beyond 400 psi as a chamber, I think I can trust it not to be crushed at 800

[irisher]

We all know that pressurized chambers bulge. I wonder if a barrel on a coax shrinks. It would be interesting to see the difference between unloaded and pressurized bore diameter,

[jackssmirkingrevenge]

It would be interesting but it would also be a bit difficult to get my vernier in there, pressurised or not

[POLAND_SPUD]

lol I know you want to build a large bore valveless launcher... go for it

[Gun Freak]

There seems to be hardly an chamber at all, it's no wonder you only got 40 fps at 100 psi

[jackssmirkingrevenge]

lol I know you want to build a large bore valveless launcher... go for it

Big bore single shot, certainly on my list... maybe something along the lines expressed here, but it would have to be some sort of captive piston device, I don't fancy the idea of destroying an airtight sabot for every shot.

There seems to be hardly an chamber at all, it's no wonder you only got 40 fps at 100 psi

Total volume is about 0.5 cubic inches C:B ratio of 1:16, you can afford it with HPA...

[Gun Freak]

Alright, I guess the hpa makes up for it, but in that diagram you posted with the grip, is that a chamber extension under it?

[POLAND_SPUD]

well wat aobut the design you psoted a year ago or so ? you know the one with the mag tube inline with the barrel and vents cut in it close to the detent... that should have enough mag capacity for 5 - 10 rounds...
I know you know what I am talking about

ohh BTW.... the weather is scorchio, don't you think ?? damn it's 30 deg C here... I am guessing it must be more than that in your 'bat cave'