I've acquired an old Classic 68 mag in need of some tlc. Unsure how many years it spent in the bottom of the previous owner's gearbag, but it gasses up fine and chrono'ed fine around 280fps... As long as I don't pull the trigger faster than 2 pulls per second. Anything faster and the sound signature changes and velocity drops. It sounds like the valve is starving for air.

So who's the culprit? Old classic valve or crappy HPA tank? I've tested the marker with a Pure Energy 48cu steelie and I know that these regs sometimes have recharge issues.