The Tactical Rifle Shooters Facebook Group not too long ago showcased tools utilized to measure case headspace ahead of and just after “bumping” the shoulder. Immediately after a case is fired, hand-loaders who complete-length size their circumstances will usually bump the shoulders back anyplace from .001″ to .0035″, based on the rifle and application. With our 6mmBR and Dasher circumstances we like about .0015″ bump.
You want the quantity of case sizing and bump to be the very same for all your brass. To assure uniformity, it tends to make sense to measure your circumstances ahead of and just after the FL sizing course of action. When we have time, we verify just about every case. Other people will just verify the 1st three-four circumstances coming out of the FL sizing die to assure the FL die setting is appropriate and delivering preferred headspace/bump.
1. Whidden Gunworks Shoulder Bump Gauge
There are a selection of tools that can be utilized to measure shoulder bump. Our preferred is a unique cartridge-particular bushing created by Whidden Gunworks. The Whidden Shoulder Bump Gauge enables you to adjust your sizing die to the preferred measurement. The bump gauge is attached to your calipers with a set screw and determines the measurement from the base to the shoulder of the case. The photo under, from Tactical Rifle Shooters, shows the Whidden Bump Gauge for the .375 CheyTac cartridge.
two. Dave Manson Vertical Comparator with Dial Study-Out
Background image courtesy Tactical Rifle Shooters inset photo from Manson Precison Reamers.
Dave Manson states: “This tool was created to make life much easier for the sophisticated shooter and re-loader by permitting precise measurement of ammunition, case, and chamber headspace. With this info, the re-loader will be capable to fine-tune clearances and fits in between his ammunition and chamber, with resultant improvements in accuracy and case life.” The functions of the Comparator are:
1. Measure headspace of factory or reloaded ammunition
two. Quantify chamber headspace by measuring headspace of a fired case
three. Make certain minimal shoulder set-back when setting up re-loading dies
four. Evaluate base-to-ogive length to assure constant bullet-to-rifling partnership.
In addition to the Dial Indicator and Stand, the $130.00 Vertical Comparator is supplied with many Datum Blocks of precise length and inside diameter (.3300″/.3750″/.4000″/.4375″). A lot more Information Right here.
three. Hornady L-N-L Headspace Comparator Technique
Hornady tends to make comparator gauges matched to the red comparator holder that mounts on your caliper. These Lock-N-Load Headspace Gauges are affordable. You can get a set of 5 gauges for $31.99. Hornady explains: “The Lock-N-Load® Headspace Comparator… gauge measures variations in brass ahead of and just after firing or re-sizing. It permits for headspace comparison in between fire-formed brass and re-sized brass.” Crucial: Hornady states: “To figure out the correct bushing diameter for your cartridge, just add the neck diameter and the shoulder diameter and divide that quantity by two. Use the bushing closest to that quantity.” Hornady presents 5: .330″, .350″, .375″, .400″, and .420″.
A single tip — We have identified the Hornady gauges may well differ a small from unit to unit even with the very same nominal size. If you have far more than 1 gauge for the very same cartridge, test each and every on your brass — you may well then note a slight distinction in your bump measurements.
four. Pistol Brass Case DIY Bump Gauge
Final is a “field expedient” set-up if you do not have any of the comparator tools shown above. A sized .45 ACP case (or other appropriate pistol case) can be utilized to measure shoulder bump. The mouth of the pistol case sits on the shoulder of your rifle cartridge brass.
Make certain the .45 ACP case is trimmed square and that it is round. We suggest you 1st run it by way of an expander, then size it, trim it and chamfer. Subsequent, take the .45 ACP case and slip it more than the neck of a fired, unsized rifle case with the primer removed. Align the two circumstances in between the jaws of your calipers and note the length from rim to rim (See left photo under).
OK, now you have the length for a fired rifle case Ahead of sizing. Subsequent, take a complete-length sized rifle case (without having primer) and do the very same factor, putting the .45 ACP case more than the neck of the FL-sized case (Ideal Photo). The distinction in between the two numbers is the quantity of “bump” or set-back you are applying to the shoulder. Right here the distinction is .0015″. The quantity of bump you need to have varies with your chamber and your load, but .0015-.002″ is a fantastic initial setting.