the Manson gauge
http://www.brownells.com/.aspx/pid=2...HICKNESS-GAUGE
there is a brace that is not shown in the picture that prevents twist
I have practised with it in several modes until I know I can get consistant measurements in different settings.
along with a Skeets bore gauge, a scale, a tape and a caliper (not in the pic) you have a compact set of tools that will give you some level of confidence when you consider a gun.
