I have to agree with what has been stated already. I would look somewhere other than the gun for the problem. I bought one a few years back that had been stored with broken paint in the barrel, bolt and hammer area for 5+ years. Disassembled, cleaned and fired like a brand new gun.
My guess is the input pressure, as well. Stick a 3.5 or 4 oz on the vertical and see how it likes that.