So I had asked a while back about a ring I was seeing around my 260 cases. I tossed the lot of brass that was showing incipient separation and had one from another lot rupture. It's a very odd looking failure that I've never seen anywhere before. The brass was on its 4th firing, 140 amax with 42.6 gr 4350, neck sized only. The rifle is a Rem 700, Krieger barrel, chambered by a local gunsmith. I'm actually thinking the rifle might have excessive headspace. What could possibly be the culprit of this type of failure?