Sinclair Shoulder Bump Gage Insert #23A, 23 Degree, 25-270 Caliber

Description

Measuring shoulder bump is one of those steps that separates brass that chambers smooth every time from brass that gives you trouble, and the Sinclair #23A insert makes that measurement simple. This one is cut for a 23 degree shoulder and covers the 6.8mm Remington SPC, giving handloaders a quick way to check exactly how far they're setting the shoulder back when they full length size.

The idea is straightforward. You thread the insert into a Sinclair comparator body, slip a fired case into it, and zero your calipers. After you size that case, you measure it again and the difference is your bump. Most bolt gun reloaders aim for somewhere in the one to two thousandths range, and having a real number beats guessing or running the die blind down to the shellholder.

What the Sinclair #23A Insert Does Differently

Rather than referencing the SAAMI datum line the way some gauges do, Sinclair bump gages index off the shoulder angle itself. That gives you a more accessible reading of how much you're sizing, and since you're measuring a change rather than an absolute number, consistency is what counts. The insert is machined to match the 23 degree shoulder so it seats cleanly on the case and repeats well from one measurement to the next.

Fitting the #23A Gage Insert to Your Setup

These inserts are built to install in Sinclair's own comparator bodies, and reloaders have long noted they'll also thread into a Stoney Point or Hornady comparator body if that's what you already own. Keep in mind the Sinclair insert runs shorter than a Hornady insert, so a standard body works great for fired and sized brass while measuring loaded rounds calls for Sinclair's larger body.

If you're chasing tight groups and consistent brass life, knowing your bump number is one of the easiest wins at the bench. The #23A keeps that process fast, repeatable, and caliber correct for your 6.8 SPC loads.