DYI wrote:Why can't you push it past 45 psi?
A hand pump (like you might carry with you on a bike trip in case of a puncture), rather than a floor one, is hard for anyone to push past about 60 psi.
I have to agree with DYI, this cannon isn't exactly optimal. It's not a bad start, but for a cannon in that size, with that valve, the energy is likely to be no more than about 15 to 20 ft-lbs, and probably more like 12, which isn't a lot.
You need a quicker valve, and more pressure to get much out of a launcher.
Muzzle energy in Joules divided by barrel volume in cc gives average effective pressure (multiplied by
145 - not 14.5 - to give units of psi), a good measure of a launcher's power relative to it's calibre and size.
Your launcher has a very low figure of ~5 psi - Compare that to an advanced combustion with a value of ~30 psi.