Today after about 100 rounds, the Sistema wasn't locking back when the last round fired. It did it intermittently. I also had several failures to feed. I was using two WC 47D 7 rounderss, two Chip McCormick Shooting Star 8 rounders and two Kimber 8 rounders. Unfortunately I didn't think to note which mags were in the pistol when it would fail. However, I'm pretty sure the Wilson's were good. The mag springs in the Kimbers and Chips seem kind of slack. Do you think that's it?