I just completed a short interesting experiment on .22 LR rimfire thicknesses.
After extensive testing of several brands & type of ammo in a Stevens Mod 44 used for 22BPCR competition, I had settled on CCI Std Velocity Target for the chickens & pigs, & Eley Match for the turkeys & rams. Although I'm aware that variations in firing pin strike and differences in rim thickness can impact accuracy, I never had a method to test either. So after reading a recent article on rim thicknesses versus accuracy I picked up a Hornady Rimfire Thickness gauge.
As expected, after measuring 100 round of each, the variation in the Eley Match was better than the CCI, but not by much. The CCI measure a medium 0.041” with a variation of +/- 0.001” or +/- 2.4%. Rotating the cartridges in the gauge & measuring again made no difference.
The Eley was better but rotating the cartridge in the gauge resulted in a 0.001” change, which was somewhat of a surprise. I.e., based on the rotational orientation, all measured 0.037” or all measured 0.038”. Therefore, the medium thickness was 0.0375” with a variation of +/- 0.0005” or +/- 1.3%. Of course the variation could essentially be reduced to zero by measuring, marking & chambering the cartridges with the same orientation, not something I plan on doing.
If you’re wondering about the rim thicknesses of "economy” ammo, 50 rounds of Win. Varmint/Plinking ammo resulted in a spread of 0.005”, Win. Wildcat Hi-Velocity spread was 0.004” and Federal Target’s spread was 0.002”. After accuracy testing all the ammo with the Stevens, the results confirmed the effect of rim thickness variations. BTW, the Federal Target & the CCI Std. Velocity Target had identical variations in rim thickness, but the CCI shot slightly better in the rifle. The Win. Varmint/Plinking was by far the worse.
So although the above results may be important when striving for tiny groups when “punching paper” with a high-quality target rifle, will it help when shooting .22BPCR silhouette? I have no idea, but it certainly can’t hurt and it does increase my confidence in the ammo I’ve chosen to use. Of course, there are other factors that affect accuracy including chamber and bore dimensions. And shooting high-precision ammo in a “mediocre” rifle is likely a waste of good ammo.
BTW, the article I referred to earlier can be accessed at
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