Have about 500 rounds through it, some walmart federals, but switched to CCI minimags. It seems every 50 rounds, on 1-2 of the rounds- the back of the shell and actually appears to be slightly crimped at the top and wont extract. Any suggestions? I like the gun and only for fun, but gets a little annoying. I am extermely meticulous and clean every 100 rounds through it, as I have been told then gunk up quickly.