Quote Originally Posted by jonny
co2 varies on the temp on the day, on a hot day you might get 1000 psi before it liquidises, on a cold day you might get 700


Did some digging and most my questions are answered but these:

I have concluded a buffer tank is fairly sensible, but how large should it be?
Is regulating it down to 250-300psi sensible or too much?

And the most important, most people say you need adaptors to use CO2 paintball bottles, where are these available from?
Size of buffer is difficult to quantify ..I've run many spreadsheet scenarios and more volume is better BUT it's a law of diminishing returns.
So ..Ummm... You must IMO have one and size... Errr...as big as is practical in your design is the best I can advise.
Your suggested pressure seems fine...perhaps a little higher.