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Setting up a full length sizing die is one of those steps where a little bit of measurement goes a long way, and that's exactly what the Sinclair #30 Shoulder Bump Gage Insert is built for. This is the 30 degree insert, machined to seat against cases with a 30 degree shoulder angle. It drops into a Sinclair or Hornady comparator body and lets you measure how far back you're pushing the shoulder every time you resize, which is the difference between brass that lasts and brass that gives you fits.
What sets these inserts apart is that they index off the shoulder of the case rather than measuring to the datum line. That gives you a cleaner, more repeatable reading of how much you're actually moving the shoulder when the case runs through your die. You chamber-fit a fired case, take a measurement, size it, measure again, and the difference is your bump. Pair it with a comparator body and a set of calipers and you've got a simple, reliable system for tracking headspace on your handloads.
As a general starting point, Sinclair recommends somewhere in the neighborhood of .001 to .002 inches of bump for bolt action rifles and .003 to .005 inches for AR-15 type rifles. Getting this right keeps your rounds chambering smoothly without over-working the brass, which means fewer case head separations and more firings out of each piece. It's also a handy way to keep ammo for different rifles sorted and to spot-check loaded rounds before they hit the range.
For anyone running a precision bolt gun or building match ammo, a bump gage setup is one of the more worthwhile additions to the loading bench. The #30 insert is a single-angle tool, so matching the insert to your cartridge's shoulder angle is the key to accurate readings. Built from quality machined stock and made to thread into the comparator bodies you likely already own, it's a small part that earns its keep every loading session.
It measures how much you push a case shoulder back when you resize, known as shoulder bump. Instead of reading to the datum line, it indexes directly off the shoulder for a cleaner, more repeatable measurement. You compare a fired case to a sized case and the difference tells you your bump.
Yes, the insert threads into a comparator body rather than working on its own. It's compatible with Sinclair or Hornady comparator bodies, and you'll use it alongside a set of calipers. If you already run a comparator setup for measuring bullet seating depth, you're most of the way there.
Sinclair suggests roughly .001 to .002 inches of bump for bolt action rifles and about .003 to .005 inches for AR-15 type rifles. Bolt guns can run tighter since you're camming the bolt closed, while semi-autos need a touch more clearance for reliable feeding. Dialing this in helps your cases last longer and chamber consistently.
These inserts are matched to a specific shoulder angle, and this is the 30 degree version machined for the smaller shoulder profile covering cartridges like the 17 Fireball, 22/6mm PPC and BR, and 204 Ruger. Because fit depends on your case's shoulder diameter and angle, it's worth confirming the insert contacts your brass on the shoulder before relying on readings. If your cartridge has a larger shoulder diameter, the companion 30A insert may be the better match.
| UPC | 050806111318 |
|---|---|
| Manufacturer |
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