Typically American brass uses a .473 inch case head, and European brass uses the correct .480 inch case head. This is fact.
What is disputed is whether or not the brass is the source of case head separations.
Case head separations are caused by lateral stress on the brass brought on by excess headspace. The radius of the brass at the case head is only .0035 difference. Measuring my once fired Winchester shows a slight bulge .300 above the case head expanding the diameter of the brass to .478 but there are no internal cracks. After running the once fired brass through a full length resizing die, that dimension was reduced to .474, so there may be some work hardening going on further back on the brass than I care for, but .002 inches of diameter reduction isn't unheard of (hence the current lineup of small base dies from RCBS).
One poster on a forum stated
This bears repeating. R-P cases in my Swedish Mausers and especially in an ag42 autoloader wouldn't last more than three loadings, Winchester fared even worse.
There is a reason that even with premium brass those who load for match grade autoloaders say "4 reloads and chuck it." Autoloaders are VERY hard on brass. Mauser's aren't exactly known for having tight chambers, and "slightly oversized" is good for reliability. I might take a drill, cotton strips, and some metal polish to the inside of my resizing die to make it a tad more oversized and therefore custom to my chamber.
In my experience excess headspace is the source of case head separation. The excess headspace allows the brass to expand forward without being stopped by the chamber, causing a lateral stress to the brass. The stress goes beyond tensile strength and the brass cracks where the brass starts to thicken near the case head. The brass near the case head is thicker so it resists stretching better than the thinner sidewall and shoulder brass.
I'll keep monitoring my brass for cracks, but I'll probably just get a neck sizing die and be done with it. Once fired brass is "dimensionally correct" for the chamber it was fired in, so sizing the neck will not work harden any of the body and allow the brass to stretch a lot less on repeat firings.
2 comments:
Back when I did more reloading (and I certainly intend to get back to it) I developed a preference for neck-sizing brass in my bolt guns. I don't recall having any separations prior to discarding the brass after five trimmings when the OAL was excessive. I did limit that brass to use in one particular rifle, and kept loads moderate.
I also found that in semi-autos, adjusting the full length dies so that the case shoulder wasn't continually pushed back, but maintained, would extend case life. Case manufacturer played a role here also; mil surp 7.62 x 51 cases lasted much longer than .308 cases in my FAL. I believe that was due to heavier construction of the case, with its attendant reduction of case capacity, that allowed more play in expansion during firing, whereas the civilian brass did have several case head separations.
You might also consider annealing your brass cases around the neck, especially if you neck size only.
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