Avoid Loose Primer Pockets

Primer Pocket Gauge

      At one time or another, most handloaders have seated a primer in a loose fitting primer pocket; and of course, it wasn't discovered until AFTER the primer was seated.   This handy little tool is designed to help the handloader verify that primer pockets have not expanded too much from previous firings.   Firing handloads with a loose primer can burn the face of your bolt, and it can have a negative affect on accuracy.  

      I recommend using this tool to check the primer pockets in every case BEFORE seating primers.   This ensures your primers will always fit properly.   You will need one of these tools for checking LR & LP primer pockets, and another similar tool for measuring SR & SP primer pockets.

Check the size of primer pockets first.

      The diameter of ALL rifle and pistol primer pockets (large and small) are both .002" smaller than the size of an actual primer.   That diameter increases very slightly at each firing, and the increase is sometimes so small that it is almost impossible to measure.

      Rifle and pistol primers only come in two different diameters . . . SMALL and LARGE.   Small Rifle (SR) and Small Pistol (SP) primers both measure .175"   While Large Rifle (LR) and Large Pistol (LP) primers both measure .210"

      The larger end of these primer pocket gauges measure .001" smaller than a good fitting primer.   When that end fits in your primer pocket - it's OK.

      The other end of these gauges measure .002" smaller than a new primer, and when that end fits, your primer fit will not be acceptable.

      Consistent readings from using a Primer Pocket Gauge depend quite a bit on the quality of your primers and cases.   Due to "acceptable tolerances" (in the relm of ten thousandths of an inch), some manufacturers make primers that are not exactly round, and the diameter of new primer pockets can also vary.   If you find that your primer pockets are expanding too soon, try keeping your handloads a bit UNDER maximum pressure; and they will last longer.   Some brands of brass are known to have harder case heads and that also helps primer pockets resist premature excessive expansion.   One of these days, I might develop a tool that tightens up loose primer pockets.   However, at this time, it is not an affordable project.

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