Concentricity Gauge

This is a concentricity gauge for reloading.

The adjustment slides have holes for 6x7mm ball-plungers. These balls provide a low-friction surface to roll the test parts under the dial indicator gauge.

The slides have a small ridge on the underside that you will need to file
to get a friction fit that allows them to slide on the rail without binding.
(The rail is part of the base and is based on the NATO dimensions for the
Picatinny rail.)

The dial-gauge cradle supports a 2" (52mm) dial indicator with an 8mm shaft. I
designed using Mitutoyo model, but tested with a cheap $10 Chinese model.

Hardware required:

4 x 6x7mm Ball Plungers (amazon pack of 20 ran under $10)
2 x M3x8mm screws
1 x dial indicator gauge (I have a $10 ebay gauge.)

Possible future improvements can be made to the cradle - maybe a smooth range
of adjustment, and support for stems of other thicknesses.

Update:
I added a slide for measuring neck thickness.
This slide has a 3mm (1/8") hol