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If you're serious about brass life and consistent headspace, the Sinclair #40 Shoulder Bump Gage Insert takes the guesswork out of setting up a full-length sizing die. This one is cut with a 40-degree taper to match the shoulder of cartridges in the Ackley Improved and 6mm family, giving you a clean, repeatable reference point every time you size.
Unlike a standard headspace comparator that reads off the datum line, these inserts indicate off the shoulder itself. That taper duplicates the actual shoulder of your brass, which squares the case head up to the caliper blade and gives you a more easily assessable reading of how much you're moving that shoulder. You measure your fire-formed case first, then size and measure again, so you know precisely how far you've bumped it back. Most bolt-gun loaders aim for around .002 inches, and this insert lets you hit that number with confidence.
The #40 is engraved with its shoulder angle and covers a wide spread of 40-degree improved rounds, including 22-250 Ackley Improved, 220 Ackley Improved, 223 Ackley Improved, 243 Winchester Ackley Improved, 6mm Ackley Improved, and 6mm/30-30 Ackley Improved. If you shoot wildcats or improved chamberings in that group, this is the insert you want in the drawer.
The insert is machined from stainless steel and installs in either Sinclair comparator body, and it also fits a Hornady comparator body if that's what you already run. Keep in mind the standard body handles brass, while the extended body is the one you want if you plan to check loaded rounds for sorting. It secures with a 5/64 hex wrench, slips onto a caliper blade, and once you let it center itself and zero out, you're ready to measure. Simple, tough, and built to give the same reading load after load.
The #40 is cut for 40-degree improved shoulders and covers rounds like 22-250 Ackley Improved, 220 Ackley Improved, 223 Ackley Improved, 243 Winchester Ackley Improved, 6mm Ackley Improved, and 6mm/30-30 Ackley Improved. Each insert is engraved with its shoulder angle, so check that against the cartridge drawing in your loading manual if you're unsure. It is built specifically for that family of 40-degree Ackley and 6mm cases.
Yes, the Sinclair bump gage insert installs in either Sinclair comparator body and also fits a Hornady comparator body. Just keep in mind that a Sinclair insert and a Hornady headspace insert contact the case differently, so they will not give identical readings. Pick one setup and stay consistent, since you are measuring a change rather than an absolute number.
The standard comparator body works fine for checking and sizing brass. If you want to gauge loaded rounds for sorting, you will need the extended length body. Either body pairs with this #40 insert for setting up your full-length sizing die.
By measuring your fired case and then your sized case, you can see exactly how far the shoulder moved and keep that number to a minimum, often around .002 inches for bolt guns. Only bumping the shoulder back as much as you need reduces how hard the brass gets worked, which extends case life and helps consistency. It also keeps your headspace right where you want it for safe, repeatable loads.
| UPC | 050806111295 |
|---|---|
| Manufacturer |
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