I have a heavily upgraded utg l96, the only part that is fairly crappy is in the cylinder, I have the cheap upgrade kit by utg. I have a metal triggerbox and reinforced heat treated sears from airsoft gi, but when I pull the bolt back, sometimes it will catch, but alot of times it wont catch, or it will and then the trigger will pull and wont shoot the rifle, then I will have to pull the bolt a few more times and slam it forward to findally get the trigger 'cocked' and then it will shoot. My main question is, are the sears to blaim, or is it the piston? The triggerbox looks fine, it's reinforced and no cracks or stress marks. I hope it's the piston because I was going to get a new one soon anyways. My other question is about a bucking, I have the pdi W hold bucking in the pdi chamber, should I get another W hold bucking, or should I switch over to a systema bucking? Also should i get the pcs nub? will it work in the pdi chamber?