just bought a mag from my field owner. was working perfectly when i got it. as soon as i got it home i just did the basic stripping to see what the bolt & power tube looked like. when i put it back together it started to leak. as soon as i air it up it starts to vent down the barrel. if i hold the trigger the leak stops. the o ring on the power tube tip looks fine as does the one under the spacer. what else could be causing this type of leak?