Test: NECO vs. Bonanza/Forster for bullet runout

[danny]

I just got a NECO Concentricity Gage and set it up per the instructions for loaded bullet runout. I got essentially 0 runout.

Brass is basic Lake City 7.62 with a Sierra 175 MK with no special prep, for my M1A.

The same round checked with my Bonanza (it is an original one) yields .0015".

I have a feeling that the NECO as set up per the instructions (with three support points) is not conducive to showing actual runout, surprisingly.

I may use it set up like the Bonanza, with only the bullet point contact and one v-block at the case head.

Set up like that, the NECO does register some runout, closer to the Bonanza, though it is only about half the reading.

Danny

 

[Bart B.]

It's too bad so many different spinners are available. None orient the bullet to the dial indicator like rimless bottleneck cartridges in chambers align their bullets to the bore when fired.

When fired in the chamber, the case shoulder is well centered in the chamber shoulder. The only part of the case body that touches the chamber is its pressure ring about 1/10 Inch forward of the extractor groove, This let's any out of round condition next to the case shoulder not move the case neck and bullet; that area is free of contact with the chamber.

Cartridges don't lay in the bottom of a chamber when fired. Most spinners have the cartridge case behind the shoulder resting on some V thing like the rear reference does. Right where case out of round conditions will skew the readings. If the dial indicator is twice as far from the rear case reference as the case front reference, the dial indicator will move .002" for every .001" change in case diameter (position) at its front reference.

If the case front reference was a round hole about the headspace reference diameter, then the bullet runout will be what it would be in the chamber.