You pushed the shoulders back too far, creating excess headspace. This can be dangerous. The COW and false shoulder method may work, but puts a lot of stress on the brass. I would start over with virgin brass and do it right.
Case seperation during fire forming
- Thread starter TheDerkster
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RockyMtnMT
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I'm not sure that it would be a good idea to seat a bullet on top of cream of wheat.
Steve
Steve
TheDerkster
Well-Known Member
It seems like a lot if you think I used bullets over powder and COW. Just for clarification, I use powder, COW, and then top with a bit of melted wax. It worked very well for the cases I didn't screw up. I may try the false shoulder method first which a few mentioned as well as pulling ejector out. If nothing else, ill buyt all new brass.
RockyMtnMT
Official LRH Sponsor
I did not think you did. It seemed like it was being recommended. I just use a bit of toilet paper in the case neck and pack it in just a bit to hold everything tight.
Steve
TheDerkster
Well-Known Member
I found wax seems easier. What do you think? Toilet paper seems easier if you don't have the wax melted, but it's awful easy to dip wax and put it in the neck.
Re: Case separation during fire forming
The false neck/shoulder will work. Never heard of placing a bullet over cream of wheat and I would never do that. That would be true wildcatting. The only other thing I would do is anneal the case shoulder after stepping up the case neck to .308, and then necking it down to 7mm. This will reduce the likelihood of any further case ruptures/separations, and help ensure the rest of the cases survive fireforming.
I use a layer of toilet tissue between the gun powder and the cream of wheat to help keep the two separated prior to ignition. I also pack a little toilet tissue on top of the cream of wheat to avoid spillage prior to firing. Works well.
The false neck/shoulder will work. Never heard of placing a bullet over cream of wheat and I would never do that. That would be true wildcatting. The only other thing I would do is anneal the case shoulder after stepping up the case neck to .308, and then necking it down to 7mm. This will reduce the likelihood of any further case ruptures/separations, and help ensure the rest of the cases survive fireforming.
I use a layer of toilet tissue between the gun powder and the cream of wheat to help keep the two separated prior to ignition. I also pack a little toilet tissue on top of the cream of wheat to avoid spillage prior to firing. Works well.
bigedp51
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Normally the softer annealed upper part of the case will conform to the shape of the chamber as below. If you were forming cases from a longer case and the new shoulder was below the original annealed section the brass could be harder and brittle. Normally a case with too much headspace is pushed forward by the ejector until it contcasts the shoulder of the chamber. If the case is extremely short the case is pushed forward until the rim contracts the lip of the extractor. And this creates excessive head clearance between the rear of the case and the bolt face. And it is the rear of the case that stretches and separates when this happens.
If you look at the center case in the photo below you can see the primer protruding. The amount the primer is protruding is the actual head clearance or the "air space" between the rear of the case and the bolt face. Meaning forward movement of the case was stopped by the extractor and the soft upper shoulder and neck section conformed to the chamber. And the case did not separate because military cases are thicker or harder than commercial cases in the base of the case.
I don't know anything about the 7mm Sherman short mag, but I learned a great deal about excess headspace as a 18 year old in the military. And excess headspace is mainly created in dimly lit bars by unscrupulous bartenders who know under age drinkers can't complain to the management.
