The Skeet's gauge and Tony Galazan's similar gauge are the weapons of choice for checking out shotguns at shows and auctions. They both extend 13" into the barrel, leaving a short section unchecked in a 32" barrel, but such a short section, if damaged or modified, would stand out like a turd on a collard leaf if it had a problem. The best ninety bucks you will ever spend. Measures chambers too. The large size will also measure standard ten gauge bores, but will not measure a ten gauge chamber.