case neck and bullet runout
Since I recently found out that I had .005 to .008 bullet runout on some 300 win mag rounds I loaded in Sep, I have become interested in bullet runout. I'm loading for hunting, but I want THE most accurate round I can load. A 1/4" inch improvement at 100 yard groupings is important to me. Just the way I am.
I've squared the RCBS dies, got a Lee decapping die, moved the expander ball all the way up in the FL sizing die, put the bullet straight up in the case before seating it and rotated the bullet 180 degrees after seating the bullet half way. I tried some 270 win fireformed brass and loaded dummy rounds. I got less than .001 bullet runout, but the runout measured on the neck about 1/8" from the mouth was .002 to .003.
How could I get so little bullet runout but have a significant case neck runout??? Which is more important measure for accuracy: bullet runout or case neck runout or both? If case neck runout is important, what can I do to correct it?