I had the same frame on my Mag for a while. I never put a lot of paint through it (maybe 1/2 a case), but I had none of the problems you are experiencing. Maybe your sear is buggered? I would try a new one before drilling anything else.
Stupid question; is there anyone near you that has a stock/functional mag? If there is, I'd suggest at least trying their frame to see if that is actually your problem.