Quote:
Originally Posted by Opalsasquatch
I've been oversizing the brass, so it stretches even more upon firing. It then gets thin near the case head
"Shuuuuuuussssshhhhh.
You can't post stuff like that, too many heads will explode."
Hillbillyreefer
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It is more likely a combination of over pressuring the brass, which forms it to a chamber that is likely over Saami Minimum, and sizing it with a FL die which cannot be set so it does not oversize the brass. It has been my experience that Federal brass holds much less powder than most other brands. A properly FL sized Federal Brass holds about 1.2 grains more powder than a Winchester brass in a 270 Winchester that I have been working on. This can result in a much higher pressure as the powder is comprssed in the Federal and not in the Winchester and this would show up on a chronograph. Aslo case dimensions may be smaller resulting in more case stretch.
It is commonly thought that setting a FL die to "Bump the Shoulder a few Thousands" will solve problems like incipient head separation that you experienced. However it only reduces case damage caused by excessive HS and not the excessive stretch at the neck, shoulder and base of a case. Neck Sizing solves this problem, except for the neck, but only if one does not overpressure the case so that it is sticky at the base.