I have a CZ 82 that fires and feeds fine, one problem, the slide will not lock back on the last round. I tried some silver bear ammo and it would lock back about half the time. If I pull the slide back by hand it lock every time. It does this with two diffrent magazines. I was thinking that maybe the recoil spring would need to be replaced as I checked the slide lock and it moves freely, changed magazines and no change, can anyone thing of anything I might try before I order a new spring and try that?