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Old June 19, 2013, 06:45 AM   #11
Bart B.
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Join Date: February 15, 2009
Posts: 8,927
Neck tension is a popular thing these days. Technically, it's just another expression of what it's all about.

In the ammo industry, bullet release force is the term used to express how easy or hard it is to get the bullet out of the case. They use tools to measure how many pounds of force it takes to pull the bullet out. How tight the case neck grips the bullet as well as the friction between bullet and case determines the force needed to do so.

With a collet type bullet puller gripping the bullet and weight added to a bucket attached to a shell holder with the round in it, the amount of weight needed to pull the bullet out could be easily and very accurately measured. In my tests of turning necks from exact thickness all the way around to just enough to remove brass 1/2 to 3/4 the way around the neck and having no more than .001" spread in wall thickness, the release force average and spread did not significantly change. Nor was there any accuracy difference through 1000 yards

7.62 NATO match ammo has a release force spec of at least 40 pounds. My measurements of both M118 and M852 ammo showed an average force of around 50 pounds with a 20% spread. Yet that ammo would shoot under 1 MOA at 600 yards, under 1/3 MOA at 100 yards. Good commercial .308 Win. match ammo I've measured has release forces around 20 to 25 pounds with the same spread; it's shot 1/4 MOA at 100 and 2/3 MOA at 600 yards.

Sierra Bullets does no prep on cases used to test their bullets for accuracy. Nor do they work up loads for a new barrel or new lots of bullets, primers, cases and powder. Their best match bullets go into 1/4 MOA at 200 yards from such cases using these procedures.

All of which to me means, unless you can shoot your stuff into no more than 1/4 MOA at 100 yards, turning case necks to exact, or nearly so, thickness is a waste of time. There's other things that'll improve your ammo's accuracy that's a lot easier to do.
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