Sinclair #20 Shoulder Bump Gage Insert, 20 Degree, 308 Family

Description

If you're reloading the 308 family and want repeatable shoulder bump numbers, this is the insert that gets you there. The Sinclair #20 is machined for the 20-degree shoulder angle shared by cartridges like 308 Winchester, 243 Winchester, 7mm-08 Remington, 260 Remington, 307 Winchester, and 308 Marlin Express. Instead of measuring to a sharp datum line that can bite into the brass, this gage indexes off the shoulder itself, which gives you a cleaner, more repeatable reading of how far you're pushing that shoulder back.

What the #20 Insert Does in Your Reloading Routine

The whole point of a bump gage is controlling headspace at the sizing die. Measure a fired case, zero your calipers, then size and re-measure to see exactly how many thousandths you moved the shoulder. Most folks aim for roughly .001 to .002 of bump for bolt guns so the brass chambers easily without getting worked harder than it needs to be. Minimizing how much you size your fired cases stretches out brass life and helps keep your loads consistent round to round.

Fitting the Sinclair #20 Bump Gage to Your Setup

This is the insert only, not the body or calipers. It drops into either the Sinclair comparator body or a Hornady comparator body, so if you already own one of those you're ready to go. A nice touch is that the insert squares the case head up to your caliper blade, which cuts out the fiddling you get with some other gages and helps you pull the same number every time.

Built to Last

Machined from stainless steel and engraved with the shoulder angle, the #20 is the kind of small tool that earns its spot on the bench and keeps working for years. Pair it with the matching comparator body and a set of calipers, and you've got a simple, dependable way to take the guesswork out of full-length die setup.