I just picked up 1k LC only headstamped brass, from BrassBombers, for $87 shipped. I have purchased 308 LC brass from them before, and have yet to find a bad case. Now I do buy the "cleaned only" stuff, and do my own prep. Basically I re-size and de-prime it, clean it in a vibrator cleaner, to remove the sizing lube, anneal it, trim it, and remove the primer crimp with a electric drill, and a chamfer tool. The results are very good 223/5.56 brass, that I get a number of loads out of.
As for "machine gun" brass, I know some of the 308 LC brass came from a military range, with 7.62 light machine guns unloading through the muzzle, and I have never had an issue with the brass. Yes, it takes a bit more effort to run it through the Redding FL SB sizing die, but once it is resized and annealed, all is good.
Squeeze