Bore Gauge

[Neil Richardson]

To be a little more specific:

This is the Galazan gauge ($450):

Professional Choke and Barrel Gauge -The world standard precision instrument used by gun manufacturers and barrel makers to measure bore diameter and choke constriction and length. This gauge is a must if you expect to be able to determine if chokes and or barrel bores have been altered. Dial indicator measures in .001 increments. Measurements are detected by expansion and contraction of three metal "fingers" under the control of the person taking the measurements. All test and set bushings and instructions included. Comes with a handsome wood case. Gauge length 22 3/4" weight: 1 1/4 pounds

This is the one on Brownells:

CSP PROFESSIONAL SHOTGUN BORE MICROMETER SET ($509)

Brownells also has SKEETS SHOTGUN BORE GAUGE $93.99