My Impact II (power plenum) has shot about 7000 shots with no problems. Recently it has detonated two shots. During these events the shot sounded like a rimfire and the projectiles went 5 or 6 mils off target. After the event the rifle shoots regularly again. The events happened about 100 rounds apart in hot weather. I have never oiled the rifle. I fill my own compressed air using two filters between the compressor and the tank. (The compressor is the Wan Yang, the blue Chinese job). The second filter is always clean after filling with no oil residues. I do lube the slugs with silicon spray.

I am shooting 25 gr slugs at 120 bar at 950 f/s in consistent half inch groups at 50 mt.

I have safety concerns. Has anybody experienced this problem? Please let me know what you think is causing this dieseling effect.