January 10, 2023 Five Cool Tools to Measure Shoulder Bump in Your CasesThe Tactical Rifle Shooters Facebook Group recently shared tools that can be used to measure the headspace of a case before and after “bumping” it. Hand-loaders who fully-size their cases after firing a case will usually bump the shoulders back anywhere between.001? and.0035?. Depending on the rifle and application, it could be.0035? to.0035? We like.0015? for our Dasher and 6mmBR cases. bump. You want all your brass to have the same amount of case sizing. It is a good idea to measure your cases before and during the FL sizing process. We check each case when we have the time. Others will only check the first 3-4 cases that come out of the FL-sizing die to make sure the FL die setting is correct. This ensures the FL die delivers the desired headspace/bump. Whidden Gunworks Shoulder Bump GaugeThere is a wide range of tools available to measure the shoulder bump. Whidden Gunworks’ cartridge-specific bushing is our favorite. The Whidden Shoulder Bulk Gauge allows you to adjust the size of your sizing die to the right measurement. The bump gauge attaches to your calipers using a set screw. It measures the distance from the base to shoulder of the case. The Whidden Bump Gauge is shown in the photo below, taken by Tactical Rifle Shooters. Dave Manson Vertical Comparator and Dial Read-Out
Background image courtesy Tactical Rifle Shooters. Inset photo courtesy Manson Precision Reamers. This information will allow the reloader to adjust clearances and fit between his ammunition chamber and chamber. This will result in improved accuracy and longer life. The Manson Comparator’s functions are: The Manson Comparator measures headspace in factory and reloaded ammunition
2. Measure the headspace of a fired box to quantify chamber headspace
3. When setting up reloading dies, ensure that there is minimal shoulder setback
4. Compare base-to-ogive length to ensure consistent bullet-to-rifling relationship.In addition to the Dial Indicator and Stand, the $150.00 Vertical Comparator is supplied with multiple Datum Blocks of precise length and inside diameter (.3300?/.3750?/.4000?/.4375?). MORE INFO HERE — Catalog page 29.3. Hornady L.N.L Headspace Comparator SystemHornady’s Lock-N.Load Headspace Comparator is simple-to-use, and very handy. Midsouth has a kit that includes a Red bushing-holder body, 5 bushings, and costs $43.43. Hornady explains that the Lock-N-Load(R), Headspace Comparator… gauge measures variations of brass before and after firing, or re-sizing. It allows you to compare headspace between fire-formed brass or re-sized brass. Important: Hornady states that the correct bushing diameter for your cartridge can be determined by adding the neck diameter and shoulder diameter to the equation and then dividing that number by 2. The bushing closest to this number should be used. Hornady offers five options:.330,.350,.375,.400, and.420. One tip: We found that Hornady gauges can vary slightly from one unit to the next, even though they have the same nominal size. You may notice a slight difference in the bump measurements if you have multiple gauges for the same cartridge. You should mark one and use it consistently. Anvil Base Kit can also be mounted to the opposite blade of the caliper. This gives your case a more stable base. L.E. Wilson Case Gage Depth micrometer Wilson Case Gage Depth Micrometer, currently $130.00 This requires precise, repeatable measurements. However, you must know your starting point. According to the manufacturer, “Every reloader must know exactly how much your Full Length Sizing Die pushes back the shoulder.” The NEW Case Gage Depth Micrometer makes it easy to do exactly that! It’s now easier than ever to measure your case’s headspace before and during sizing. The Depth Mic allows for you to slide the micrometer over the top of your Gage with your case in the Gage and take measurements. Micrometer has a graduation of.001?. The Case Gage Depth Micrometer has a zero value of.100. on the scale at our factory. We include a Gage Block to allow you to test Zero and adjust if needed. Pistol Brass Case DIY Bulk GaugeLast can be used as a “field expedient” setup if you don’t have any of the comparator instruments. To measure the shoulder bump, you can use a sized.45 ACP (or any other suitable pistol case). The pistol case’s mouth is located on your rifle cartridge brass. It is recommended that you first run the case through an expander. Then size it, trim it, and chamfer. Next, place the.45 ACP cartridge case over the neck of an unsized, fired rifle case. Align the two cases with your calipers. Note the length from rim-to-rim. Next, take a full-length rifle case (without primer) to do the same thing. Next, place the.45 ACP over the neck of your FL-sized case (Right photo). The difference between these numbers is the amount you apply to the shoulder. The difference is.0015?. The amount of bump that you need will depend on your chamber and load. However, it should be between.0015 and.002? This is a good starting setting.
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