Sinclair #20A Shoulder Bump Gage Insert, 20 Degree, 338 Lapua

Description

If you're loading for the 338 Lapua Magnum and want tight, consistent headspace, this Sinclair #20A insert is the piece that takes the guesswork out of setting up your full length sizing die. It's machined from stainless steel with a 20-degree taper that mirrors the shoulder angle of the 338 Lapua (and 338 Federal), giving you a clean contact point that squares the case head up to your caliper blade for accurate, repeatable measurements every time.

How the #20A Bump Gage Insert Earns Its Keep

Rather than measuring to the datum line like a lot of headspace tools, this gage indicates directly off the shoulder of the case. That means you're reading the actual change you're making to your brass, which is really what matters when you're chasing consistency. The common approach is to measure a fired case, zero your calipers, then size and re-check until you've bumped the shoulder back the amount you want. For bolt guns, somewhere in the .001 to .002 inch range is the usual target, and tools like this make that number easy to hit.

Fitting the 338 Lapua Insert to Your Setup

The insert drops into either Sinclair comparator body and locks down with a 5/64 hex wrench, then the body clamps onto your caliper blade. If you already run a Hornady or Stoney Point comparator body, these inserts will fit that too, though you'll want Sinclair's longer XL body if you plan to gage loaded rounds rather than just brass. Each insert is engraved with its shoulder angle, so there's no second-guessing which one you've got in hand once they're mixed in the toolbox.

It's also a handy way to keep brass sorted if you've got more than one rifle chambered in the same cartridge, letting you track where each batch sits. For anyone serious about brass life and accuracy out of a big 338 Lapua, this is a small part that pulls real weight at the loading bench.