Concentricity (Bullet Runout)

[vinconco]

I think a lot of runout is caused by a slight "banana" bending of the case due to wall thickness variations after it is shot. This can actually be measured with the NECO gauge and in the past shooters would mark their case heads to orient the rounds when chambered to get the bend in the same place for each shot.

 

[bsumoba]

I measure just to measure, but whether I see near 0 runout or 3-4K of runout, I still shoot it. However, that being said, if I get 3-4K of runout, I will make adjustments to my reloading, most likely in the die setup. Goal is somewhere around 1K, but I don't go crazy if I see some in the 2K range. I usually test the few few and if those look good, I just run a bunch of brass.

Like others said, I try to focus on consistent seating pressure and since I run 4-5K of neck clearance and jump almost everything, I think all that combined helps. I have not seen a concrete difference between near 0 runout and one that is 3-4K in concentricity when it comes where the bullet hits the paper.

 

[vinconco]

The NECO gauge will measure wall thickness inside the case body. Cases with more wall thickness variations in the body area will also show greater bullet concentricity variations. This is generally an issue after the case has been fired and resized due to "springback".