I don’t think I explained myself very well. It made sense to me while I was typing but after rereading, it wasn’t the best. My measurements were all base to datum point on the shoulder on fired brass.

The 30-06 range brass varied .015” at the shoulder. I surely didn’t think chambers varied that much. I would suspect some of the rifles it was fired out of may have headspace issues, but then maybe they were fired out of semi autos and stretched a little more.

The 6mm brass that necked up and fired in my 257 Roberts, didn’t fireform all the way on the first firing. It is still .005” shorter at the shoulder than the actual 257 Roberts brass fired in the same rifle. The 6mm brass will need one more firing before it is fully fireformed to the chamber.

The 7x57 brass was range brass I had gotten from Wes. I full length sized and trimmed it all. My rifle is on the upper edge of acceptable headspace, it would be considered borderline excessive headspace. I loaded some super light loads with 4227, to let my kid get used to the rifle, I also loaded some with standard powder charges ( on the lighter side). The brass that was loaded with the super light charge was .010” shorter at the shoulder than the brass that was loaded with the standard powder charges. The lighter loads didn’t expand the brass enough to fill the chamber so they are substantially shorter at the shoulder than the other brass.

The most confusing of all is the 280 Ackley brass. I fireformed some standard 280 brass in my 280 Ackley chamber. Half of it has been shot a second time. The measurement difference, to the shoulder, between the once fired (fireformed) brass and the twice fired, was .007”. I didn’t even get close to a full fireform on the first firing. My new Hornady and nosler 280 Ackley brass was closer to my chamber dimensions than my fireformed brass.

When brass is fireformed, shoulders blown out etc, the overall length always shrinks. The issue I was having with short was at the shoulder. I really thought I was getting a better fireform than I actually was.


JTD