Re: H & H Concentricity gage or Bersin or ???
Folks have been trying different ways to bend bullets in rounds with too much runout for years. Every one of them involved pushiing on the bullet to straighten it up. Not a good idea in my opinion.
My own tests have shown that such " bullet straightening" hurts accuracy. The bullet's been bent enough in the case neck that it's held with a different amount of tension. If you want to straighten the bullet, you had better straighten the neck, too. Bullets are aligned with the case neck axis when they're seated. I don't think that should change.
I've taken 30 caliber ammo and put their necks in a .338 diameter bullet puller with the high point of runout marked on the case so it's where I can press on it. A little practice tells one how much the case has to be pushed to bend the neck just the right amount. Tighten the collet just enough to hold the loaded round case neck firmly, not tight enough to size the neck and bullet down.
Shooting such "neck straightened" ammo shows only accuracy improvement. Use a bullet puller collet of the right size. If one's not available, well, maybe you could make one or fashion a collar to put over your case necks to fit a collet that does work.
Use gelded full length sizing dies (no balls) and your case necks well be much straighter. Depending on how the case is referenced (rested?) at its contact points in the runout tool, the numbers will vary. There's no such thing as a perfectly round case (chamber either, for that matter). Especially when V-block types are used and the out-of-round condition at the case shoulder will corrupt any reading one gets.
Tool and die experts dealing with metrology and precice measurements of mechanical things will tell you that the best way to support a cartridge to check it for bullet runout is in V-blocks touching the pressure ring and datum line about mid point in the case shoulder. These are the two points on the case that position it in the chamber. The extractor pushes the case sideways so the pressure ring stops against the chamber at the back end and the case shoulder centers in the chamber shoulder as it's pushed there first by the plunger style ejector and second by impact from the firing pin.
Last edited by Bart B; 02-22-2010 at 08:20 AM.