Quote:
Originally Posted by lclund1946
Looking more closely at the picture it could be possible that the pressure, on the primer, was not enough to push it back against the bolt face. This would allow the primer to flow around the firing pin by roughly as much as the primer was seated into the pocket. You could check this by measuring the primers seating depth near the rounded outside diameter with your calipers. Where it has flowed out would likely be 0.000" seat depth. Normally primers seat 0.005" into a properly uniformed primer pocket.
I don't think changing brass will help unless the primer pockets are larger which may allow primers to move back more freely. The most likely cause of this is that the Batt action has a stronger firing pin than necessary for the pressure you are running. This does not mean that the pressures are not fairly high as low pressures are usually indicated by a cratered primer. Measuring the 0.200" base datum with a micrometer, looking for the largest reading, on a new case and comparing it to a fired one may give you an indication of low pressure but the chronograph reading against a known pressure load would be the best.
Let us know how what you find.
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260 Rem: After posting this I got to thinking that this could be caused by a heavy firing pin in a situation where you are using new brass, or brass that is not fireformed. In that case the donut on the primer would be protruding past the brass at the base like in the case of a weak firing pin and measurable the same way. I took a look at the picture with the brass in the calipers, which I should have done before, as it clearly shows that this is happening. Going to a thinner/softer shouldered brass may help but likely not unless it has less Headspace. In cases with very little taper, like the BR's, bolt thrust is much less than in more tapered ones and the firing pin is likely holding the case forward and the brass is forming to the chamber walls further stopping it from moving back to the boltface. This would result in the brass not fully fireforming and leaving the excess HS that allows the primer to flow around the firing pin. Perhaps you can try to fireform this brass by reducing the charge a bit and do a full jamb into the lands which may hold it back on the boltface?? However this is not really a pressure problem and perhaps just repeat firings will do the trick. However I may be totally out to lunch on this as well as I have never encountered this before.