Re: Started neck turning
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Victor N TN</div><div class="ubbcode-body">Turning the case necks has nothing to do with runout. You are trying to make the case neck walls an even, thinner thickness.</div></div>
I disagree here. While I don't have any "before" and "after" results, in measuring Lapua case necks, I find about 2% - 4% have differences within the case neck of greater than .003". When you bushing size, you drive that imperfection to the inside. It is hard to imagine a bullet having less than .003" runout seated in one of those pieces of brass with large thickness variation. If you can imagine, it is not so much that the bullet doesn't get seated square, it is more that in those cases, the bullet will actually get seated off-axis to the center of the cartridge. It will show runout even if it is seated perfectly squarely. Of course, it probably makes it harder to seat it squarely as well.
Of course, the solution there is to cull those pieces out, which is why I measure cases, but if you think about those extreme cases and apply it to pieces with an already small amount of variation, say .001" (about 70% of Lapua 308 is .001" or less), and turn it into immeasurable variation, I have to believe that it helps concentricity.
I agree however, that prior to fireforming, a case might exhibit runout and turning the necks will not help this because the brass itself may be banana-shaped prior to firing. You want to turn before fireforming, so the time to check for runout for those who want to turn is after first firing.
If there is runout then and the necks are turned, the runout could come from a crooked chamber, problems with the seater, etc., but you can scratch neck thickness variation off of the list. Otherwise, it is alive as a possible source of runout.
