low/no power-mini metal coax

[Pyro Ninja]

Normally I wouldn't post about a "small" problem like this one but I am getting really tired of screwing around with piston valves.
Well I have a couple of "guns" I need to finish before the end of the holidays, anyway I have built a small full metal coaxial.
Originally it was going to have a diaphragm valve, but with that failing a decided to go with a piston.

I made a piston from a small rubber cork by -ghetto machining- it to the right size.


SPECS

Chamber- 15mm galvanized steel
Barrel- 9mm id aluminum
Pilot valve- 1/4 ball valve
I know, not very detailed specs









The piston seals perfectly, but when I pilot it, there is only a small spurt of air out the barrel.
I can only get it up to 100psi, but the power should be more then what it is.

[jackssmirkingrevenge]

I can only get it up to 100psi, but the power should be more then what it is.

Not really, for such a miniscule chamber volume at 100 psi I would expect it to be of very low power.

[Pyro Ninja]

Can't say I am pleased with your answer Jack (I thought you would come up with some kind of super effective answer to solve my problem )
So there absolutely nothing I can do to improve power?

I guess i'll have to buy a shock pump when I make a bit of money.

In the second last picture the copper pipe around the aluminum is only a short length just to relieve some of the stress on the piston.

[jackssmirkingrevenge]

If you decide to keep the current setup as it is, then higher pressure is really the only solution for more power. With your all metal construction it would be safe to go to the 350-400 psi a shock pump can give you, and if you keep pilot volume low a shrader will be enough to both fill and pilot the launcher.

[Hotwired]

Umm...

I can see perhaps 2-3mm of clearance round the inner tube as the chamber.

I suspect I might have slightly more chamber volume in my high presure test rig which is literally a 15mm compresson elbow, a ball valve, a barrel and a schrader.

That's filled to 400psi with a shock pump and even up to a 1m barrel it's still got really naff power, but that wasn't what it was about ^_^

Be generous! Give yourself a non-thimble-sized chamber for Boxing Day and all will be well

[carter]

that is a tiny chamber. is there any chance that you could extend it if you wanted to?

[Pyro Ninja]

Well the chamber is approximately 15mL so that would give me 15 cubic cm of air.
The barrel is about 12 cubic cm
What kind of power should I expect at say, 200-300psi

[jackssmirkingrevenge]

What kind of power should I expect at say, 200-300psi

two-three times what you're currently getting. 15mL is the sort of volume I use as a minimum for my 6mm calibre mini-pistons, you should be looking to increase it for this project.