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Old December 29, 2012, 09:07 AM   #8
Bart B.
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Join Date: February 15, 2009
Posts: 4,826
5whisky, your rifle's bolt face may be out of square enough to make the case head enough out of square when it's fired. Rechambering that round with the high points of bolt face and case head together will cause binding. There's not enough room in the chamber to allow that case's longer dimension between the head's high point and shoulder to fit in without the bolt closing hard.

Most benchresters stopped neck sizing their fired cases some years ago. They moved to full length sizing with dies having a bushing that sizes the neck just enough to hold the bullet. After depriming fired cases and cleaning them, they set the full length bushing die in their press to set the fired case shoulder back about 1 thousandth. The die also sizes the case body down about the same amount. The sized case now fits the chamber without binding.

Two wonderful things happend witht their accuracy when they started using such dies. One is the bolt never binds on a chambered round. Anyting that happens, the bolt does not seat in exactly the same place for each shot. The other is there's a bit of clearance all around the case body (except at the back end where they all are pressed against the chamber wall by the extractor) as the case shoulder perfectly centers in the chamber shoulder when the round's fired. The other is the size of their largest groups got smaller. Their smallest ones (those that win the matches and sometimes set records) remained the same size. So the overall accuracy of their ammo got better; the most it missed their aiming point got smaller. Their aggregate scores (average of all fired groups) got better.

Competitors shooting rifles in positions where they rifle's held to their shoulder (not free recoil, untouched by benchrest folks except for their trigger finger) in standing, sitting and prone have been full length sizing their ammo for decades. And some have shot test groups smaller than current benchrest records properly testing their ammo.

The best dies one can use today for their bottleneck cases are those full length ones made by Redding and RCBS with a bushing set to size all of the neck down so it's a couple thousanths smaller than a loaded round's neck diameter. Even a standard full length sizing die, set up and used right, typically produces better accuracy than any neck only sizing thing. Sierra Bullets uses Redding dies of this ilk resizing their fired cases testing their bullets for accuracy. Their best match bullets shoot 1/4 MOA in their 200 yard test range from cases so sized.
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Last edited by Bart B.; December 29, 2012 at 09:12 AM.
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