The issue began when I heard a subtle grinding noise when I fired my gun. BTW, it is a KWA M4.
I immediately stopped playing and disassembled the gear box. When I was trying to remove the upper receiver, it wouldn't allow me because the piston hadn't moved to the relieved position. I'm not sure if this is the case for other M4 guns, but you can't split the receiver on the KWA one if you don't fire it in semi-auto before as the receiver tabs come in contact with the piston rails (the thing the piston rides on).
Anyway, with this in mind, I concluded that the sector gear teeth was not properly seated in the piston's teeth because I had fired it in semi-auto before disassembling and it didn't move the piston. Yes, it did make the subtle grinding noise when I fired it.
Can someone tell me if I'm correct in my assessment and if so, why? Did I time the gears wrong? I put the little notch at the 1 to 2 o'clock position, but I probably did something wrong. Maybe the tappet plate?
Edited by Doctor Kajita, 04 October 2008 - 10:40 PM.