Used upper questions.

[Herzo]

You can check your fired brass for an incipient separation by putting a sharp point on a paperclip and bending a 90 degree angle a out 3/16" from that end. You can use the hook to reach into the case and feel for a groove 1/8" or so from the bottom of the case. Once you feel the groove, you should toss that lot of cases. It may take a couple of firings for the groove to show up. If you catch the problem after the first firing and adjust your resizing die, you may get more.
If you or a friend happen to have a 7.62 x 39 AR, you can use the bcg from it to check the headspace in that it should be a type I.