We have some very perceptive folks in this thread....... may I please interject a thought?
I think the generally accepted reasoning behind close neck clearances stems from two sources, addresses two problems. #1, the close neck match allows neck brass to hold up for a long time because it's not being worked so much and #2 the neck tolerance acts to guide the bullet straight into the rifling. I minimizes "inbore yaw".... And by "close neck tolerance I mean basically anything under 4 thou total clearance, more likely .003 or less.
If I asked 100 accuracy minded folks, or even 1000 whether or not having .003 total neck clearance on a 6PPC was detrimental to accuracy..... I strongly doubt that even ONE of them would reply "yes, that's TOO MUCH CLEARANCE!"
"thin to win" and Jack Neary have done a good job of showing that .003 clearance is fine as regards accuracy.
right??
NOW...... with 3 thou total clearance that means .0015 per side which in my estimation means that that bullet WILL BE JACKED OVER to one side or another by at least a thou and a half when the bigger hammer shoves it down the bore......
"no-turn" specs are generally set around .002 over the loaded round neck diameter, maybe .003.
Now, disregarding the ugly burr on the mouth of new brass can anyone come up with a compelling reason why no-turn necks SHOULDN'T shoot just fine?
(I happen to have 6BR's in 5 neck sizes, 6PPC's in 4 sizes and 300WSM's in 4 sizes so have some pretty strong opinions on the subject and I'll state right out front that I see NO GAIN in thinner necks FWIW)
EXCEPT that, when forming very heavy necks....... like 308 from 30-06 cases there can be a set of issues not related to accuracy.
Them's my thoughts anyway, if anyone cares to comment.