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Setting up a full length sizing die by feel is a good way to overwork your brass or risk headspace that's off. The Sinclair #45A Shoulder Bump Gage Insert takes the guesswork out of it. Machined with a precise 45-degree taper, this insert mirrors the shoulder angle of wildcat cartridges that headspace on a 45-degree shoulder, so you can measure exactly how much you're bumping the shoulder back when you size a fired case. It's the kind of tool that pays for itself the first time you watch your brass last longer and your groups tighten up.
Rather than referencing the datum line like a traditional comparator, this gage indicates off the shoulder of the case itself. That gives you a more accessible, repeatable reading of how much material you're actually moving during resizing. The insert drops into either a Sinclair comparator body or a Hornady comparator body and locks down with a 5/64 hex wrench. From there it clips onto a caliper blade, and you measure a fired case, adjust your die, and recheck until you land on the bump you want. For most bolt guns, a shoulder bump of about .001 to .002 inch is the sweet spot, while AR-type rifles usually like a touch more, closer to .003 to .005 inch.
This one is built specifically for 45-degree shoulder cartridges up to 30 caliber, which puts it squarely in wildcat and improved-case territory. If you're running custom chambers or Ackley-style brass with that steep 45-degree shoulder, this is the insert that matches up. It also doubles as a handy way to keep brass and loaded rounds sorted if you've got more than one rifle chambered in the same cartridge.
Keep in mind you'll need a comparator body and a set of calipers to put it to work, since those are sold separately. Pair it with the gear you already have on the bench and you've got a precise, no-nonsense way to control your sizing every single time.
The #45A is machined for cartridges with a 45-degree shoulder up to 30 caliber, which covers a range of wildcat and improved-case designs. If your brass headspaces on a steep 45-degree shoulder, this is the matching insert. Check your cartridge drawing in a loading manual to confirm the shoulder angle before ordering.
Yes. The insert itself drops into a comparator body and clamps onto a caliper blade, so you'll need a Sinclair or Hornady comparator body plus a set of calipers, both sold separately. You'll also want a 5/64 hex wrench to secure the insert in the body. Once you've got those pieces, setup is quick and the readings are repeatable.
Instead of referencing the SAAMI datum diameter, this gage indicates directly off the shoulder of the case. That gives you an easier, more accessible reading of how much you're sizing. The key with this tool is consistency, since you're measuring the change in your case before and after sizing rather than an absolute headspace number.
For bolt action rifles, a shoulder bump of around .001 to .002 inch is a common target, while AR-type rifles generally run better with about .003 to .005 inch for reliable feeding. Keeping that bump minimal extends brass life and helps with accuracy. Use fired cases from your own chamber as your reference point when setting the die.
| UPC | 050806111264 |
|---|---|
| Manufacturer |
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