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Old February 3, 2013, 02:08 PM   #19
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 5,476
Gotta enter this thread 'cause there's a bunch of myths put in print.

First off, I think one could use a long established load that's been used to win matches and set records. With new cases and the right components put together the right way with the right tools, if one's rifle doesn't shoot under 1 MOA at 100 yards with that stuff, it ain't the ammo's fault.

Second, this old theory that a "perfect fit" of case to chamber is best for accuracy is usually championed by folks that don't understand how a rimless bottleneck case fits the chamber; both when first loaded and when fired. When fired, which is what counts, their front end's perfectly centered in the chamber up front on the shoulder and the neck, if well centered on that shoulder, will be perfectly aligned with the bore. Doesn't matter how much clearance there is around the case; the back end's pressed against the chamber opposite the extractor anyway. How else would brand spankin' new mass produced ammo fitting all sorts of chambers shoot 1/2 MOA or better at 600 yards? That's the norm with good lots of mass produced Palma ammo fired in .308 Win. match rifles.

Third, the most popular myth of neck only sizing; finally busted by benchresters. While shoulder fired match rifles have been shooting just as accurate as benchrest rifles rested on bags for decades, they've done so with full length sized cases with proper dies and techniques. Benchresters finally moved from neck sizing to full length tools and methods a few years ago. While the size of their smallest groups have remained the same, the biggest groups they shoot are a lot smaller; overall better accuracy. Of course one should always measure their accuracy by the largest groups for a given load as those are the ones that show what happens when all the variables add up in the same direction. Ever wonder why Sierra Bullets has been full length sizing their fired cases since the 1950's to test their stuff for accuracy and nobody shoots 'em as accuate as they do?

Fourth, small muzzle velocity spreads and uniform case neck tension are not nearly as important as other internal ballistic stuff. That's been proved by arsenals and others loading match ammo and the best lot has often had a greater velocity and release force than those not so accurate. Bullets being a few ten thousandths bigger than the barrel's groove diameter plus powder choice and charge producing uniform pressure curves are way up on the list. Primers uniformly igniting powder is also important; hot magnum ones are typically not as good as milder ones.

Fifth; the myth of getting exact bullet seating depth. It's amost impossible to get a constant seating depth or distance to the rifling. Bullet ogives are not all the same shape for a given lot of them as the metalurgy ain't perfectly uniform. They all have different ogive shapes a couple thousandths different from each other. Plus, rimless bottleneck cases position the bullet in the chamber relative to its distance from the case shoulder. Case headspace (head to shoulder reference point) will have a few thousandths spread so bullet distance from case/chamber shoulder, and the start of the rifling, will also have a few spreads. Even with absolute zero tolerance from case head to bullet ogive reference point. Want zero seating depth spread? Seat bullets out to jam into the rifling and seat back a few thousandths when the round's chambered. This has been popular for decades with Sierra's; not so with Berger's that need a few thousandths jump.

There several others, too. . . . .
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