I realize that there have been a number of posts about BAR 10's and related guns slam firing, and I have read many if not all of them. I still have questions.
I got the gun from Airsoftgi and it started working ok. Then I opened it up, cleaned the hop up bucking and the barrel, cut the air brake halfway down, and put some teflon tape on the threads of the cylinder head. I made sure everything was lubed properly and all the parts were put together properly. It may not be important, but after that the gun could barely crack the top of a coke can with .20's. Then after about a magazine of rounds, it started slam firing
I tried just about everything from the troubleshooting guides with limited success, but it always eventually starts slam firing again. I actually got some stainless steel M3 screws (along with some split lock washers) to replace the pathetic ones it came with (to attach the trigger box to the receiver).
The screws are tight (but not over-tight), the bolt moves smoothly enough and doesn't wiggle, the sears are almost brand new with no cracks and very little wear, There is little if any wear on the piston, and I tried shimming the spring guide stopper. Actually I also fixed the pin that the trigger sear swivels on because it was allowing the trigger sear to wiggle to the side; that really helped and I got a few magazines worth of shots out of that, but then it started slam firing again!
What is the proper way to shim the spring guide stopper?
BTW, another thing that bothers me is that there is a substantial gap between the trigger box and the receiver, even with the screws on tight. Do you think this might be the problem? Might I need a new trigger box? At some point, I'll either get a Zero Trigger or M trigger, but I don't currently have the finances. (How much does the m trigger cost anyway? I looked and thread and couldn't find it) (or what about a V-trig?)