I personally use mostly IMI and some Lapua brass in the .223 and 223AI. But several yrs. ago I sold a mint, early Rem. varmint 223 to the guy I shoot with. And he uses nothing but pick-up range brass in that thing, whatever non-military is out there, several different headstamps, un-sorted. That gun shoots quarter inch groups, I've seen them. His hit ratio is very high and I've never seen him miss a prairie dog. I wouldn't use that stuff and don't need to anyway, but still........
