I saw a Post about this today, but now can't locate it, wanted to add a few comments regarding my experience of re-loading mixed cases.
When re-sizing mixed cases it was necessary to make adjustments to the die for different case brands to get the desired case head-space consistent, which I like to do..
The Commercial cases required less die depth than the Military cases.
My M1A has a chamber head space of 1.626". The rifle preforms best when the cases are full length re-sized to 1.620" max.. My M40A1, which is the more accurate of the two rifles, likes the cases to be short of chamber head space only .003".
Testing the Mixes cases in the M1A was disappointing when compared to cases of the same brand.. Fed. .308 Win. cases out preform all the others consistently. With the Fed. cases it is a good idea to toss them after three firings. I have run them farther only to experience case separation at the case head to often to continue past three uses..
The M40A1, testing mixed cases, preformed somewhat better than the M1A, but unacceptable groups sizes none the less..
At the risk of being stoned, my load is: 168 SMK, CCI #4 primers, 39.5 IMR 3031. COAL of .085".
Recently purchased a new expensive case trimmer, I discovered that by reversing the cases it is possible to crank the handle and true- up the base nicely, the M1A likes to pull the rim out of alignment during extraction, this extra labor has benefits if you are group greedy like me.. Art L.