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Old January 16, 2013, 07:45 AM   #4
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 4,834
I've had zero problems reloading ammo with absolute zero case prep. Even brand spankin new cases will shoot 1/3 MOA at 100, 1/2 at 300 and 3/4 at 600 and at 1000 yards 1 MOA; all with half way decent brass. Good brass will shoot even better. Case weight can have a spread as much as 2% and great accuracy is still easy to get, but sorting to less than a 1% spread's a waste of time. There's a greater spread in the energy exact powder charge weights or primers have than what a tiny difference in case volume has.

All that's needed with bottleneck cases is to full length size fired cases with bushing dies that reduce case body diameters and set fired case shoudlers back no more than about 2 thousandths and have their neck diameters a couple thousandths smaller than that of a loaded round. Use a case headspace gague (RCBS Precision Mic or equivalent) to measure case headspace; set fired case shoulders back no more than 2 thousandths.

Case length from head to mouth needs to be at least 10 thousandths less then chamber length; don't go over SAAMI specs. And cases can have several thousandths spread in their length; a 5 thousandths spread is common in good commercial .308 Win. match ammo that shoots unde 4 inches at 600 yards.

Regarding the issue of trimming case length to all having the same exact length to get consistant neck tension, consider the following. With a bullet that's held by 2/10ths inch of the case neck length, for every .002" difference in that length, that's a 1% change in how tight the neck grips the bullet. How many readers have actually measured the force it takes to pull a bullet out of turned case necks with exact dimensions, then looked at the percentage spread form least to most amount of force to do it? Once you've done that, you'll feel just fine with a .005" spread in case/neck length.
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Last edited by Bart B.; January 16, 2013 at 09:23 AM.
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