Concentricity gauge

[markm87]

I sorted off some Factory Black Hills .308 once and shot the straightest ammo head to head with the worst runout ammo in the boxes at 100 meters. (SMKs/tangent ogives) And the bent carrots shot pretty much the same accuracy at that distance that the straightest rounds did.

I too have spun a bunch of rounds on the concentricity gauge, and then let it gather dust on the shelf.

 

[mikecr]

A long time ago it used to be suggested that eccentricity caused bullets to point off center with bore line, and this would engrave off center. That bullets would travel down a bore off center and snap to their own center on muzzle release (hurting accuracy).
I believe the many posts about runout not mattering counters that theory.

Most freebores are tighter than common runout, and can only allow a small skew no matter how bad you make ammo. I think that when bullets are neck released they immediately find least resistance to travel.
The bullets could rattle into engravement though, and there I believe optimum CBTO relieves this condition.
I posted earlier that case runout will matter when you run out of chamber clearance for it.
Hard to prove these things directly, but we can watch for tests passing & failing.