My only experience in fire forming was transforming 7.62x39 to 6.5 Grendel. Well a modified 6.5 Grendel. THey are supposed to have small rifle primers whereas the 7.62 cases use a large rifle primer. It may make a difference for precision shooting but they work fine for mine. I used IMI, Isralie Military Industries brass and it works fine. This was initially for a couple of AR 15 rifles in 6.5 Grendel. The resized loaded cartridges for fireforming fed from the magazines and even at much lower pressures cycled the action and gave me nicly formed cases.
