March 11th, 2007

Rimfire Run-out: Shocking Test Results

Too often we rely on luck and “voodoo” to pick the best rimfire ammo. Shooters resort to testing batch after batch of ammo in hopes of finding the “holy grail”. What we’ve learned, in testing a 17 Mach 2, is that some of the accuracy issues with rimfire ammo CAN be quantified, and the “mystery flyers” can be explained. Using a Nielson Brothers Concentricity Gauge, we tested lots of 17 Mach 2 ammo from Eley and CCI. Most of the rounds had run-out of .002″ or .003″. However, we found some rounds had run-out as high as .009″ (See video). That’s shocking. A cartridge with .009″ run-out is a guaranteed flyer that will kill your group. Interestingly, when cartridge run-out was .004″ or higher, you could clearly see the bullet tip was way off-axis–confirming the results of the gauge. Using the Nielson Gauge we could quickly sort bullets in .001″ increments. For match purposes, you should cull anything worse than .003″ run-out. By sorting for .0015″ run-out or less, we were able to reduce our average group size by 30%. More importantly, we eliminated most of the unexplained fliers that were landing well outside the main group. The Nielson Gauge works for both 17 Mach 2 and 22LR. And, with different inserts, you can measure 17 HMR and 22 magnum rounds.

Click to Watch Rimfire Run-out Test Movie (1 mb .wmv file):

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