skeeter7mm,

Sounds as if this is the first time that you've experienced case head separation. Well it Will almost knock your socks off. It take your eye out and is one of the best reasons I can think of for wearing shooting glasses.

It's almost unbelievable how many things have to happen, in order, for that case head to separate. First of all, while I don't care for Remington cases, the brand of your cases had nothing to do do with the separation. I haven't read all the replies you've gotten, and if I step on anyones toes, I apologize. Please believe me that it was nothing personal.

1. Case head separation is an example of head space problem. Either the nut who chambered the rifle was lose, or the nut who adjusted your sizing die got it too tight. I wish I had a dime for every belted magnum case I've neck sized in the last 50 years plus or so. I've always neck sized only. By the time chambering became a problem, I replace the cases, andthis usually got me about 8 to 10 shots per case. Those shots were full power loads. I have a target shot with 68.5 grains of IMR-4831, 140 grain Sierra #1910, CCI #250 primer that won a month long 3 shot, smallest group contest. The groups were fired from a bench at 200 yards. My group measured .581" to win the 4x scope division. Another target of the rifle was with the 150 Sierra SBT, CCI #250, 68 grains of IMR-4831 with a velocity of 3087 fps. Four shots measure .198" at 100 yards. Still another target for the same 150 Sierra SBT, same powder and primer for a velocity of 3124 fps that measures three shots at .098". It just so happens all three of these targets were fired with a 7MM Rem. Mag. M-700 Remington rifle. All were neck sized cases, but it was with threedifferent rifles.

2. Once the firing pin strikes the primer, and before the powder starts to burn, the case is driven as far forward in the chamber as it will go.

3. Once the powderstarts to burn and chamber pressure starts to climb the thinest part of the case starts too expand first. Since the thinest part of a case is at the mouth of the case, it expands first.

4. A ring of brass moves up the case as the pressures increase and come in contact with the chamber wall.

5. Until the demand that the case expand due to increasing pressure fails too matchthe ability of the brass to keep up with the rearward movement of the case head. Then separation occurs.

6. The case cannot move rearward in the camber due too it being held in place by gas pressure.

7. Once separation occurs, chamber pressures start to drop. But it is not uncommon for escaping gas to mess things up a little first. With reduced pressure the front of the case shrinks, allowing gases to flow between the case and the chamber wall which results in those dents you found and why they were so sooty.

Sounds like a wholelot of stuff going on in a very short time doesn't it?
I hope that this is of some help.