Concentricity is important or I'll lose sleep at night. But more important is shooting the difference and determining if there is any between the 2 setups. Is the partial neck sizing keeping the brass closer to my chamber dimension thus leading to better accuracy?

Lemme know.

Ammo concentricity has a mathematical relationship with group size as published NRA A.A. Abatto.

But ammo is inserted in the chamber with random rotational orientation.

Cut chambers with eccentricity are fixed orientation.

While we shoot ammo that is 0.0050" concentric and that matters, we chamber while dialing in to 0.0001" and that does not matter.

The reason we are backwards is ammo is recurring effort and chambering is a one time effort.

We have a wrong way caveman heritage industry to make cheap arrows and expensive bows.... because making arrows is so much work.

*MATHEMATICAL SOLUTION

A laterally displaced center of

gravity moves through the rifle bore

in a helical (screw) path. The pitch

of this helix is the pitch of rifling,

and its radius is the lateral displace-

ment of the center of gravity. On

leaving the muzzle, the center of

gravity continues in the direction it

had at that point. For example, if it

leaves at top of the bore and rifling

is to the right, the departure will be

to the right. The bullet travels ap-

proximately 2l.5" in a 24" barrel,

making 2.15 turns in the 10" twist

of rifling. The number of turns

shows the orientation on emergence

compared with that in the chamber

before firing. The angle of emer-

gence is that angle whose tangent is

2 pi times the lateral displacement

divided by the rifling pitch. For

.004" point displacement and I0"

rifling pitch, the tangent is 1/8(2·pi)

(.004)/l0 and the corresponding

angle is 1.1 minutes.

The displacement on target from

this cause is proportional to the

range and can be obtained without

noting the angle. For example, ,004"

point displacement gives in l0"

rifling pitch, so far as this mecha-

nism goes, a target displacement at

100 yds. (3600") indicated by the

proportion .00l· pi /10=X/3600, from

which x =1.1".