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If you reload for the 220 Swift and want to stop guessing how far you're pushing the shoulder back, this is the piece that makes it a measurable, repeatable number. The Sinclair #21 bump gage insert is cut with a 21 degree taper to mirror the shoulder angle of the 220 Swift, so when you seat a fired case into it, the gage reads off the shoulder itself rather than a single datum point. That taper is the whole idea here, and it gives you a cleaner picture of exactly how much you're sizing each case.
Shoulder bump matters because over-sizing your brass works the case, shortens its life, and can throw off headspace. Keeping the shoulder set back just enough extends brass life and keeps your reloads consistent. A common starting point is around .001 to .002 inches of bump for bolt guns and a touch more, roughly .003 to .005 inches, for semi-autos like the AR platform. You check a fired case, size one, then compare the two numbers and adjust your die until you land where you want.
The insert is made from stainless steel and installs into either the Sinclair comparator body or a Hornady comparator body, so if you already own one of those you don't need anything extra beyond this insert and a 5/64 hex wrench to lock it down. Clamp the body onto a caliper blade, let it self-center, snug the thumb screw, and you're measuring. One tip worth knowing: make sure fired cases are de-primed or have primers seated flush, since a protruding primer will give you a false reading.
The gage is engraved with its shoulder angle so you can confirm you grabbed the right one, and because it doubles as a quick way to tell sized brass from loaded rounds, it's handy if you run more than one rifle in the same chambering. For the 220 Swift reloader chasing tight, consistent headspace, this is a small part that does a big job on the bench.
No, this listing is for the #21 insert only. It installs into a separate Sinclair comparator body or a Hornady comparator body, so you'll need one of those if you don't already own one. Once the insert is in the body, you lock it down with a 5/64 hex wrench and clamp the body onto your caliper blade.
The 21 degree angle matches the shoulder of the 220 Swift cartridge. Instead of reading off a flat datum line, the tapered insert indicates off the actual shoulder of the case, which gives you a clearer measurement of how much you're sizing. That's what makes it well suited for dialing in shoulder bump precisely.
Yes. The Sinclair bump gage inserts drop right into a Hornady comparator body as well as the Sinclair body. Keep in mind the Sinclair and Hornady inserts are cut differently, so they won't produce identical readings, and for measuring shoulder bump on loaded rounds the Sinclair XL body is the one to use.
A common recommendation is about .001 to .002 inches of bump for bolt action rifles and roughly .003 to .005 inches for AR-style semi-autos. You measure a fired case, size one, and adjust your full length die until the sized case reads where you want it. Setting the shoulder back just enough helps extend brass life and keeps headspace consistent.
| UPC | 050806111189 |
|---|---|
| Manufacturer |
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