November 20th, 2015

Check Primer Pocket Diameter and Depth with Handy Tools

Primer depth diameter gauge brass cartridge

One side of this gauge is the “go” side which quickly tells you the depth of a primer pocket, whether any crimp is properly removed, and whether the primer pocket is loose. If it feels loose on the “go” side, use the other end of the tool, the “no go” side, to test to see if the primer pocket is too loose to hold a primer. If the no-go slides into the pocket, then you know to junk that brass.

Primer Pocket Growth and Useful Case Life
Repeated firings at stout pressures can cause primer pockets to grow in diameter. This can create an unsafe condition if your primers are not seating properly. Are your primer pockets “good to go”, or have they been pushed to the point of no return? Do you really know? Many guys try to gauge primer pocket tightness by “feel”, as they seat the primer. But that method isn’t precise. Now there’s a better way…

Primer depth diameter gauge brass cartridgeThe folks at have created a handy set of precision-machined gauges that let you quickly and accurately check your primer pockets. These gauges (aka “gages”) are offered in two sizes — for large and small primer pockets. A two-piece set of both large and small gauges costs just $19.99. These gauges let you quickly measure the depth of a primer pocket, and check if the crimp has been removed properly. Most importantly, the gauge tells you if the primer pocket has opened up too much. One side of the gauge has an enlarged diameter plug. If that “No-Go” side fits in the primer pocket, you should ditch the case — it’s toast.

CLICK HERE to order Small and Large Primer Pocket Swage Gageā„¢ Set from

Precision ground from O-1 tool steel, The Ballistic Tools primer pocket gauges serve multiple functions. The inventor of these tools explains: “I created the prototype of this tool for my own use in brass processing. I needed a way to quickly and easily measure primer pockets that was reliable and did not require wasting a primer. This tool has been indispensable for me and I would never go back to the old method of uncertainty and guessing.”

Product tip from Boyd Allen. We welcome reader submissions.

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