If crimping rifle ammo increases accuracy, then one believing such should convince the competitive shooters winning matches and setting records without crimping to do so. These people know better than to crimp rifle ammo case mouths onto bullets. Even the military arsenals learned that crimping .30-06 match ammo case mouths degraded accuracy in semiauto rifles; they quit that back then. None of the military teams handloading ammo for their 7.62 NATO service rifles ever crimped in a bullet; they new better and it wasn't needed. Even commercial and arsenal match ammo used in these match rifles didn't have crimped in bullets; their people knew better.
Crimping adds another huge variable in pressure curve shape and size; not good for accuracy. Crimping also distorts jackets without crimping grooves therefore unbalancing bullets; it ain't uniform all the way around; another bad thing for accuracy.
Do what you want with your reloading tools and techniques. If you have to crimp bullets in for best accuracy, then I think you're doing something wrong with your tools and techniques that crimping partially corrects. Use the right tools the right way and crimping ain't necessary.
I wonder why respected suppliers of benchrest reloading tools don't list a crimping die.
And the right one properly set up and used, full length sizing dies produce more accurate ammo than any neck sizing ones do.
Case necks resized correctly grip the bullet hard enough to keep it in place without crimping. Even in heavy recoiling magnums, case neck tension alone's enough to do just fine.
Last edited by Bart B.; October 3, 2012 at 10:37 AM.