July 20th, 2007

TECH TIP–Poor Man's Headspace Gauge

Here is a simple, low-cost way to get reliable readings of case headspace when you “bump” the shoulder back on your 6BR, .243, or .308 Win brass. Credit Boyd Allen for this tip. First, you’ll need one .45acp case, with primer removed. Make sure the .45acp case is trimmed square and that it is round. We recommend you first run it through an expander, then size it, trim it and chamfer. Next, take the .45acp case and slip it over the neck of a fired, unsized case with the primer removed. Align the two cases between the jaws of your calipers and note the length from rim to rim (Top Photo, striped case).

OK, now you have the length for a fired case. Next, take a sized case (without primer) and do the same thing, placing the .45acp over the neck of the FL-sized case (Bottom Photo). The difference between the two numbers is the amount of “bump” or set-back you are applying to the shoulder. Here the difference is .0015″. The amount of bump you need varies with your chamber and your load, but .0015-.002″ is a good initial setting. By using this simple tool, you can avoid bumping the shoulder too much. This will also help you set-up the depth of your full-length die to get the proper amount of bump each time.

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