Measuring shotguns is important, but it’s tricky. It can take three hands to measure drop and cast; as for pitch, you’re supposed to put a gun in a doorjamb and measure the distance from the barrels to the wall. Measuring inside barrels is harder yet. There’s the old trick of seeing if a dime fits in a 12-gauge muzzle, or you can use a pocket choke tool, which tells you the diameter of the muzzle and nothing more.
In short what you need to measure a gun properly are the right tools. Enter the Shotgun Combo Gauge and the BoreMaster, from Robert Louis Company. Between the two you can measure almost anything about a shotgun you’d like to quantify.
I’ve owned and used the Combo Gauge forever. It consists of a sturdy aluminum ruler with one square at the end and another that slides back and forth like calipers for measuring length of pull. A “drop meter” ruler lets you measure drop at any point on the comb, cast and, with the included protractor, pitch. You can get a second drop meter as an accessory—so you can measure drop at comb and heel simultaneously—which is nice but optional. The other accessory, an extension, is more of a necessity.
Bolting the extension onto the ruler adds 23” of length, and a magnet holds the Combo Gauge onto the rib, freeing your hands to fiddle with drop meters and protractors. The Combo Gauge sells for $150, the extra drop meter is $39 and the extension is $79.
The BoreMaster lets you peek inside the barrels. It’s a spring-loaded digital caliper that reaches 6” into the barrel and measures bore, choke and chamber diameters. It does take some practice to get good readings from the BoreMaster.
An optional kit consisting of an O-ring, a .025”-thick calibration strip and a plastic cap that fits on the end of one probe lets you measure barrel-wall thickness. And while the tool works, barrel walls still should be checked by a gunsmith, if you are planning barrel surgery. The BoreMaster sells for $279 with the 12-gauge calibration ring.