From Warthog,

I was using the Dillon dies for .308 which came with my Dillon 650 reloader. I had some chambering problems which was traced to a little too much taper crimp. The die pushed down on the end of the brass causing the shoulder to bulge out a little. I replaced the die with the Lee die, which uses a collet. The collet makes contact with the shell holder, and moves up into the die with the brass. The taper in the die squeezes the collet into the brass, so there is no downward pressure. Problem solved! Not all Lee dies use a collet.

I have not done any tests to determine if a crimp helps or hurts. I read is some of the load data books that state that a crimp can help, but I see many here believe it can hurt. Perhaps it depends on the powder. Some types might have to reach a pressure/temperature before the bullet is released to insure complete combustion and reproducibility. Some powders ignite better than others.


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Warthog,
We've never had to go beyond IMR 4064, RL-15, IMR 4895 and most recently Ramshot Tac to find excellent shooting loads out to 500yds. With several different shooters and rifles we've conducted blind chambering tests to see if the crimp helped/hurt the consistency of both 1st shot cold bore and grouping at the same distances. After shooting close to a thousand rounds between us no one found any difference in accuracy out to the same 500 yds. So I only crimp when I feel that the bullet may have to little neck tension or a shallow seating depth and am comfortable that the results will be satisfactory under any condition. By the way, we conducted our tests at 200,300 and 500 yds. Three Remington 700's and 2 Savage 10 FP's were used in the test, all with Factory Heavy barrels. The rifles had as little as 570 rds to a max of 3750 rds fired thru them. Each rifle was tested with it's own accuracy load.

Slim