Today I decapped and polished 110 cases for my 8x57mm Turkish Mauser. This is the rifle I shoot in the high power match, and these are my match cases.
This is not virgin brass..... far from it. It's so far from virgin that I'd have to wash my mouth with soap just describing their level of 'experience'. They are headstamped MM 7.92 42, and that makes them of Canadian manufacture from 1942. Yes... I said 1942. I shoot 66 year old cases in my match rifle. Get over it. I'm cheap.
The thing is... on examining the cases as they came from the polisher, one had a blemish going around the circumference of the case. That is one possible sign of an incipient case head rupture, and has to be taken very seriously.
I sacrificed one of the cases to the diamond saw, and sectioned it for examination of the case walls. I was shocked to find the brass shows absolutely no sign of stretching at all. This after being fired from the original military loading and another six or seven of my match loads which involved a case overstuffed with IMR 4350.
I attribute this to neck sizing almost every time, with one full length thrown in at the start.
On another note, for polisher media I tried something new. Solid plastic pellets made for rock tumbling and polishing. Maybe a sixteenth of an inch around, with a seam that's slightly rough. I gave them a spritz of Ballistol before the polish session, and the cases were mirror clean in an hour or so.
What makes the plastic pellets so special as a media..... when it gets dirty I'll be able to rinse them in hot soapy water, dry them in the sun, and keep right on using them with no end in sight. That makes them cheap....