Good old Federal. I have a bunch of it from 200 pcs 1f X39 I bought, probably 80%+ FC. Atleast one had a sharp line around the middle of the body where they like to fail. I've had AE 223 brass do this on the 1st reload (2nd firing) and stopped using it in semi autos. I once had an XCR somehow eject both halves of a seperated case. I have no idea how. The next round chambered and fired so the front could not have been in the chamber. Both halves were on the bench.