I'm using an ExpertHPA 13" bottle with 1200 psi reg, no problems. Mine's gone through several iterations, the most recent is in the post Robert linked too. On a hot day, CO2 pressure can go well over 1200 psi, although I don't remember exactly where the ceiling is. If you really want to know, post the question on the main forum, I know Steve in NC has the info readily at hand.
These things are addictive, aren't they
? I started with ONE .177 QB 79 a few months ago, it's since been changed over to .22, and the only parts I'd need to build another one is a stock and trigger assembly. This one is a learning experience and practice for a .25 I'm planning. After that, who knows
? Maybe a big bore, ala Jack Haley and Randy Mitchell. Later.