Home Forums Hunting & Shooting Ask The Gunwriters concentricity problems caused by seating

Bushrat,

Thanks for your observations—and your experiences with unsquared case mouths match mine.

The one tool I’ve found that helps straighten bullets without screwing up neck tension is the Tru-Angle, because it bends the neck slightly, instead of just pushing the bullet around inside the neck. But even then the run-out can’t be too bad before straightening. I’ll use it to correct a couple thousandths of run-out, but not much more.

What is your personal run-out correction limit? And why do you stop there? What have you found by correcting run-out "too much"?

The limit depends on the rifle. When I got my first of several concentricity gauges around many years ago, an RCBS Casemaster, the instructions said big game rifles rarely benefitted from bullet alignment less than .005”, and varmint rifles less than .003”. Over the next few years I found that to be basically correct, though it depends on the chamber. A custom big game rifle with a minimum SAAMI chamber can often benefit from .003” runout, or even less, but a factory big game rifle probably won’t. In my benchrest rifle I try for as close to zero runout, because it definitely benefits from as little as possible.

Aa a result of all that, for most big game rifles I don’t try to correct with the Tru-Angle that’s more than .007”. Above that and the corrected rounds still won’t shoot as well as uncorrected or minimally corrected rounds, probably because neck tension is compromised. With most varmint rifles I don’t try to correct runout more than .005”, for the same reason.

Dunno if that answered all your questions!

Thanks for taking to the time to respond. Your answer was exactly what I was looking for.

I finally had a chance to experiment a bit with the problem and the RCBS seating die I referred to in the original post. I neck-turned a few cases using my old Marquart neck turning tool which pretty much eliminates run-out on the neck O.D. and creates consistent neck thickness. I seated a few bullets with lock ring locked in place and got the same .003-004" run-out. Then I seated a few bullets but with the lock ring completely loose which resulted in just about zero additional run-out. As the bullet enters the case mouth the die flexes a bit but at least with those bullets, a Sierra boat-tail match, it made a huge difference. Perhaps it will be different by using conventional hunting bullets, but will report later. Thanks all who have shared.