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Old December 3, 2009, 11:03 PM   #8
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 16,194
To get consistent crimp you will need two things: Same case length and same wall thickness coming at the mouth. This will mean brass that was trimmed uniform when new and has the same load history, and it will probably mean brass that is the same brand and maybe even the same lot.

Once you have that, the crimp is going to be as consistent as your press can make it. I like to see the brass bite into lead to prevent setback. For that purpose I measure the brass over the bullet just below the crimp, then look to see it is about four or five thousandths smaller immediately below the case mouth. If I have that, I believe I have an adequate crimp, and whatever it is exactly, that it will be the same from round to round.

If you want to replicate crimps precisely, you will need to get some chucking reamers and make some precise holes in some eighth inch metal plate in 0.001" increments and find the right hole for each brass brand that gives you the same height from the case head to the plate each time. It's a lot of trouble to go to, not to mention the expense of the reamers. If you headspace on the bullet, as mentioned earlier, that will set adequate start pressure up. Then you are relying on the crimp mainly to hold the bullet through feeding and its exact dimensions are less critical.
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Last edited by Unclenick; December 4, 2009 at 08:27 AM.
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