Re: .308 military brass
I've been there and done that myself. I had several cans of 7.62 that I shot out of a M60 and resused the stuff for M14s.
The brass was more difficult to resize than commercial.
The problem is two fold;
1. the brass is made to be stronger than commercial and
2. It got shot out of a generous chamber and was most likely extracted while still under partial pressure.
I had short case life with the stuff. Mostly split necks. That is a good idea about using two stages to resize the brass, once full length resized and then small base. The case runout would probably be better too.
I've learned that the "sniper rifle" competition crowd will reload their cases in a similar manner but the step down they use is with neck bushings if they need to reduce more than .003-.004 thousandths. They say this significantly helps in runout control at the neck.
Just one more tool of knowledge to throw in the mental toolbox.