I have one 18" Barrel Gauge (Dial--Analog Type) with precision calibrating fixture. This Gauge measures 10--12--and 16 Ga. barrels. Our gauges are used by many Choke Makers and Gunsmiths, as well as Barrel Makers and Those that do Shooting'Clinics' !!! Accurate to .0005 !! $150.00 + $25.00 Shipping.---PM me here only.--Thank You ! Includes easy instructions.