Re: what to do with cases with excessive neck run out?
Update, I ran less beat up new 300 Rem ultra mag brass through a standard RCBS die just over the sizing ball to make it more uniform 30 cal opening. Neck run out was typically 0.002, surprising me. I then ran it over the redding die mandrel to neck up to .338 size. It has a longer sizing mandrel compared to the RCBS (0.375 vs. .053 of visualized brass contact area.) The force needed on the handle of the press to neck up seemed more consistent having made the 30 cal opening more consistent before necking up in size. I think I will do this again if for no other reason than it made me feel warmer inside. It may also have helped run out, but I was also using brass that was in better shape.
I picked up run out when necking up. I tried rotating, I tried running the mandrel up higher in the die, I floated the stem, I floated the die, I floated both, etc. I was unable to improve my run out in this step - .001 to .008. (But, much better than before with rougher brass)
Due to the force involved in necking up, I could have picked up run out in several places. Case just a little out of line in shell holder, shell holder not exactly square to ram causing some cant of the case, ram of press wobble as I push brass up, base of brass not square to rest of case - allowing the stem to float should help in these areas as I understand things. It may also be due to neck wall thickness variances causing the neck to stretch out a little more on one side than another. Maybe the Redding mandrel is not as good as the Sinclair. In my case, I'm guessing it was mostly the the brass and how and where it wanted to stretch- thickness related in the neck and possibly other areas of the case to a lesser extent as the case body of this new brass is not touching the die body when the neck is going over the sizing mandrel.
Anyways, I ended up with 53% of my brass .004 and under, 80% under .006, and 100% under .008. Still not sure if that is good or bad yield on new rem brass when necking up. I am going to finish loading some of my best cases, try to correct any bullet run out with a Hornady concentricity gauge, and shoot a few rounds this weekend!
Once again, please point out any misunderstandings in my thinking. I realize that I may not have it all straight and welcome your thoughts. Thanks for you help and your time. Casey