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Old February 8, 2017, 12:26 PM   #26
Unclenick
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Join Date: March 4, 2005
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Jim,

I thought you meant the chamber shoulder, not the bullet shoulder. Sorry for the confusion.

Yes, using both roll crimp and headspacing on the bullet produces the highest start pressure combination. A lot of us moved over to the taper crimp, not because of trying to headspace on the shoulder, but to put off case mouths splitting and then having to toss the brass earlier, as the roll crimp causes. But it never produced equal start pressure.

If anyone has a copy of the old NRA book, Handloading, you find on page 66 a photo of the barrel hood with the case flush with it, as I put in position 3 on my drawing (counting from the left). It was shown in response to a question from a fellow with a match accurized 1911. In those days we still built up the hoods and link lugs on standard barrels by welding filler metal onto them, and then filed and scraped them until the fit was right. Extending the hood made the chamber longer. The fellow asking the question listed on page 66 had a chamber that was 0.9176" from the back end of the hood, which is too long for headspacing on the mouth of a case that is 0.8980", much less one that is 0.8920".

If you then go to page 112, where there is an article on .45 Auto loading, it gives both the taper and roll crimp, stating either is acceptable, but the bullet it illustrates the roll crimp with has a crimp groove used and not enough metal from there to the bullet shoulder to reach the lands in a long chambered gun. This is the kind of setup that is headspacing on the extractor hook, and it was very common, just not optimal. Optimal requires starting with a short chambered barrel, fitting it, then reaming to final headspace.

From an accuracy standpoint, the main thing is to get the bullet bearing surface at leas a short way into the throat for alignment. Contact with the throat by a lead bullet also helps provide some additional resistance for the firing pin blow.
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