Yea, a lot of people have said that. With their inline regs both my thumpers have zero problems with hpa, although jd said even though he uses an inline reg his preferred co2. like I said though, I (along with five folks I've teched thumpers for) have had no problems. just make sure you give everything a nice clean and lube (properly lube, lightly with the right lubricant - magnalube or vaseline for instance) before you try running it on hpa. good luck!