Cheap Tricks: Measure Shoulder Bump with a Pistol Case

October 28th 2021. Here’s a low-cost, simple way to measure case headspace. Simply “bump” your shoulder back on the 6BR,.243 Win or.308Win brass. This tip is courtesy of Boyd Allen. First, you will need a.45 acp (or.40 SW) case with primer removed. You should trim the pistol case squarely and round. It is a good idea to first size it, then trim it and chamfer. Next, take the.45 ACP (or.40 SW), and place it over the neck a fired, unsized riflecase with the primer removed. Align the two cases with your calipers between their jaws and take note of the length from rim-to-rim. (See photo below, with the striped case). Now you can measure the length of a fired rifle case before you size it. Next, take a full-length rifle case (without primer) to do the same thing. Next, place the pistol case over the neck (Bottom 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. This simple tool will help you avoid bumping your shoulder too much. This will allow you to set the depth of your full length die to achieve the right amount of bump every time. Other types of pistol brass work too: Some people have tried this method, but they prefer to use.40 SW or 10mm brass. Smaller pistol cases may be easier to fit into their rifle cases. It works great! You can use whatever pistol brass case you prefer for your rifle brass. The results were very consistent with.45 acp brass, but the method can also be used with 10mm or with.40 SW brass. Make sure that the pistol brass has been properly sized, trimmed and chamfered.
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