Welcome to the forum and the meter looks good so far.
You might be wondering what
Starman meant by "
because of cold weather concerns you should design a meter that fills at around 60 psi".
Take a look at the Spudwiki page on
propane. There is a graph that shows the pressure in the propane cylinder as a function of temperature. On a cold day at ~35F the pressure in the cylinder is about 60 PSIG. So when it is that cold your meter can't be pressurized above about 60 PSIG.
If you are not planning on shooting when it is that cold (or if you keep the propane cylinder near 70F) the cylinder can pressurize your meter to higher pressures. At 70F the cylinder is at 110 PSIG.
As to how big your chamber should be ...
* assuming your limiting the meter to 60 PSIG (which I think is unreasonable low, I would figure on 90 PSIG or so, which increases your chamber volume by 50% compraed to the 60 PSIG limit)
* assuming you don't want to double-inject fuel (which allows the chamber to be twice as big as a single injection)
* the chamber size is about right for a handheld gun. Could be perhaps 50% bigger and still be reasonable as a handheld.
Even though this will be a moderate sized gun it'll still have considerably more muzzle energy than say a 0.22 rifle, so it ain't no toy. There will be enough recoil load that you
must brace the barrel to the chamber. The recoil load will put too much stress on the elbows if the elbows are all that links the chamber to the barrel.
You are of course installing a chamber fan? The fan will boost performance more than the meter, or any other mod of a 1X combustion gun.
