steel co2 barrel sealing cannon design help

[daccel]

I’ve made a few ball/sprinkler valve pvc pneumatics before and I’m working on a co2 piston valve design now. The goals for this design are portability, accuracy, high velocity (without going too light), low volume. This is what I’ve come up with so far. It consists of two 2” steel chambers 24” long, one on either side with a ball valve on each so that two shots can be taken without refilling. Then there is a barrel sealing piston valve, and a 1” barrel 4’ long, 1’ of which is perforated that vents out into the 3” pipe surrounding the barrel as an integrated silencer. From what I’ve read on this site, there’s ‘no replacement for displacement’ when it comes to silencers, so under the 3” tube is a 2” tube connected by holes along its length. I’m thinking of regulating the co2 to 500 psi, which, from what I gather here, should be safe with steel. The projectile will be a ~5”x1/4” steel dart spin stabilized with fins in a sabot. It will likely be breach loading, or there wouldn’t be a point to having two chambers. GGDT puts a 35 gram projectile at 625ft/s.

These are some questions I can’t seem to find answers to by searching:
-Will the force of the piston slamming back be enough to move the gun before the projectile leaves the barrel and throw off accuracy?
-At higher pressures can the rubber seal on the piston get cut by the pipe or do you just use a harder rubber?
-What is a good exhaust valve to use, keeping size to a minimum?
-I found 1 ¼” aluminum tubing in home depot (forgot to check for sch. or rating) would that be safe to use for a barrel even though the pressure will be quite high in the first section of it? I would rather not use steel because I’m trying to minimize weight given there’s already two steel chambers. Also, going to a 2” barrel shows 100 more fps and 100 less psi at the muzzle, would that make silencing easier?
-Does the silencer setup I have make sense, especially the second pipe underneath? I’m not sure that the co2 will have time to enter it before the projectile leaves the barrel. Also, is plastic safe to use for the silencer tubes, GGDT shows the pressure being down to 175psi by then.

Any other thoughts on how I could better achieve those things (portability, accuracy, velocity, volume) would be great! Sorry about the diagram, drawing is not my forte.

[jackssmirkingrevenge]

The projectile will be a ~5”x1/4” steel dart spin stabilized with fins in a sabot.

You don't need a spin stabilisation on a finned dart, it's the reason why APFSDS ammunition designed for rifled tank barrels have a "slip ring" on the sabot to prevent spin being imparted on the projectile.

Will the force of the piston slamming back be enough to move the gun before the projectile leaves the barrel and throw off accuracy?

Due to the limited acceleration the piston develops (no need for more than 0.25" of piston movement in your case) the force will be insignificant compared to the action-and-reaction recoil forces.

At higher pressures can the rubber seal on the piston get cut by the pipe or do you just use a harder rubber?

If you shape the lip of the barrel correctly there shouldn't be significant wear, though of course the harder and thicker the rubber the better.

would that be safe to use for a barrel even though the pressure will be quite high in the first section of it?

Unless your projectile is really REALLY can't-move-it-with-a-hammer tight, yes.

Also, going to a 2” barrel shows 100 more fps and 100 less psi at the muzzle, would that make silencing easier?

Yes

Does the silencer setup I have make sense, especially the second pipe underneath?

If the holes joining the pipes are at least equal to the area of a 1" circle, it will make a difference. if i were you I would include baffles around the muzzle area though.

Also, is plastic safe to use for the silencer tubes

I've used DWV tubing for silencers on 400 psi pneumatics, you should be fine.

[BOMBOMBOMB]

well because this website is about learning hi have a few questions. Really nooby ones but i need to find out sooner or later.
What i sch. and how does it affect the pipe. could i please have a link of how to make a piston and how it works. And is it possible to make your own C02 canisters? really nice sounding gun
Cheers Nato

[Marco321]

well because this website is about learning hi have a few questions. Really nooby ones but i need to find out sooner or later.
What i sch. and how does it affect the pipe. could i please have a link of how to make a piston and how it works. And is it possible to make your own C02 canisters? really nice sounding gun
Cheers Nato

A little searching would help with a piston valve, there is a sticky on pneumatic discussion, click This link for info on piston valves

Now to your query on Sch. Sch is short hand for schedule which means wall thickness. Now, don't confuse Sch with pressure rating, Sch.40 doesn't mean pressure pipe, it just means the walls are a certain thickness. PN x or x PSI or x BAR mean pressure rating, where x being a number.

I hope to see this gun finished . I like your silencer idea.


EDIT: Forgot to mention your CO2 canisters lol. You could weld one together, but it would have to withstand pressures in the order of 1000psi. This will be a challenge, it would be cheaper and easier to buy one.

[BOMBOMBOMB]

Ok one more question is it possible to make your own C0s cartridges and how do you and what with do you refill them.
This is kinda off topic i apologize

[Marco321]

Ok one more question is it possible to make your own C0s cartridges and how do you and what with do you refill them.
This is kinda off topic i apologize

I just answered that. You can make one if you want to make a pressure vessel capable of holding at least 1000psi. Then to get it filled at a CO2 place it would probs need to be approved by the correct people. You fill it with CO2 (carbon dioxide NOT COs). You have to get it filled at a proper place by proper people. It will cost around $160 US to buy a decent tank a regulator and its not that expensive to fill up.

[daccel]

Thanks JSR, but on the spinning part, why is the fletching on arrows set at an angle to induce spin if it doesn't help stabilize its flight? With the APFSDS could it more have to do with how it acts on impact than in flight?

[jackssmirkingrevenge]

you might have a point there

[daccel]

I thought so . Another question that just occurred to me, with the suppressor on the barrel will a suppressor on the exhaust be necessary/useful?

[daccel]

I did a quick model in sketchup . Ditched the 2nd chamber because I want this to be really clean looking, otherwise the design is pretty much the same. I can't build this until christmas vacation, such a long wait!

[jackssmirkingrevenge]

Another question that just occurred to me, with the suppressor on the barrel will a suppressor on the exhaust be necessary/useful?

I think chaos fitted one to his S400, it depends on your pilot volume - if you keep it to the bare minimum it shouldn't be an issue. Slick design btw, reminded me vaguely of this Russain offering.