If it has a modified, after market magazine, that will be your issue. Possibly the way the mag is pinned is causing the follower to drag on the last case coming out, slowing it enough that it won't clear. Try a factory part (magazine assembly) and see if that cures the problem. Back when we could load as many rounds as we wanted into our magazines, virtually no one used Tapco mags, 30 rounds with failures doesn't beat 10 for sure, now Tapco mags make even less sense.