I'm using Crosman CO2.
I am not sure where exactly the leak is coming from, but it leaks down the barrel. I managed to get 16 rounds out of another magazine after taking it apart and trying to tighten down everything in the gun.
You mentioned the seal on the puncture pin- do you mean a pin in the magazine or in the gun? The CO2 pin in the gun seemed plenty tight to me, and the o-ring looks just fine.
Regardless, I ended setting it up for the remote line and was still having problems, although chops/barrel breaks instead of air issues- another weird issue (as described below). Guess I have to figure that out first, but I was tired of messing with it so just threw it back in my car and ran my A5 for the day...
Last time I took it out on the field, I ended up chopping a ball towards the end of the day. I took the barrel out, ran a squeegie through it (BACKWARDS) and continued having issues with chops/breaks. I figured that although the detents didn't look bad, I might have messed them up with the squeegie. I took my gun apart, and put in new detents. The gun was previously chronoed at 280, but when I went to chrono, I was chopping/breaking about every 4th ball using a hopper. I took the barrel out, and I had shot the detents out of the barrel... as in, broke off the part that actually extends into the barrel.
Like I said, brand new detents and I broke them trying to chrono the gun. I know I didn't install them backwards or anything, but is there some trick that I'm missing here?