Use 6mm Comparator as Rimfire Gauge

Here’s a great way to use an existing Stoney Point-style bullet comparator to measure smallbore case rim thickness. The Stoney Point tool, now sold by Hornady as the “Lock-N-Load Bullet Comparator“, comes with a red comparator body into which inserts of various calibers can be fitted. If you have a 6mm (.243) insert for the comparator, you can use it as a “poor man’s” rimfire rim-thickness gauge. It works perfectly for 22LR and 17HM2–just drop the rimfire round to be measured in the hole, and then slide the unit against the caliper jaws. For a slightly tighter fit, use the .223 insert and ream VERY slightly. But we think you’ll find the standard 6mm insert is just about perfect. We were able to get repeatable readings to about .0005″. This is an ideal “Zero-Cost” adaptation of a popular tool.

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