I shoot Tula steel case .308 in my PTR-91. It flings the brass into low earth orbit, so it may as well be steel case. The fluted chamber probably helps extraction, I dunno. Some would say the fluted chamber destroys brass, but that I dunno either. The steel stuff works just fine in the PTR-91, so I'm happy. What I don't like is getting a steel case inside my shirt! It will leave a welt. Seems to hold the heat way better than brass.