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Measuring .22 LR rim thickness

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 was aware that variations in firing pin strike and differences in rim thickness can impact accuracy, I never had a convenient method to test either.  So after reading a recent article on rim thicknesses versus accuracy I purchased 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 and chambering the cartridges with the same orientation, not something I plan on doing.

If you’re wondering how “economy” ammo compares in rim thickness testing, 50 rounds of Winchester Varmint/Plinking ammo resulted in a spread of 0.005”, Winchester 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 Winchester 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 http://www.nxtbook.com/nxtbooks/nra/ssusa_201805/index.php?utm_source=newsletter&utm_medium=insider&utm_campaign=0518#/22

Wayne

Wayne,

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.

I have the gauge and have measured and shot a lot, and I mean a lot of 22 ammo. First years ago,  in my lever guns, 39A and 1897 Marlin with a Winchester 52 barrel and then  my 44.5s then in a CPA with a Douglas barrel and now in my CPA with a Shilen ratchet barrel. My take, sloppy chambers will shoot the best ammo into groups big enough to hit a truck but a quality rifle, great triggers, the best match chamber with quality ammo will shoot lights out. I stopped checking the rim thickness on the Laupa Center X and Midas plus because it is not necessary.  The quality is there.  Other brands from major manufacturers is a different story. I am not sure what is going on with them but the big names, Federal, CCI, Winchester etc. seem to have slipped in their quality control and their ammo is off my buy list.  Just because it says "Eley primed" doesn't mean it is Eley.  There is some "Eley primed" crap coming out of Mexico. Some of the shooters using the big name brands are using ammo that is ten years old when the quality was still good.  Only problem with it is if it is not stored in a cool environment the lube will harden or evaporate off the bullets and then it is worthless.  But then even the best ammo must be keep out of the heat or it is no good. You can "feel" the lube on good ammo.  RWS and real Eley is still very good ammo. You need lights out ammo,  the best rifle and a very good spotter to shoot this 22 BPCR game.  .22 ammo is unique and the building of it is not in our control so shoot different brands until you find one that shoots well in your rifle.  Nuff Said.

Dick

Bottom line, in .22BPCR competition, you cannot have too much accuracy. You are shooting a very small diameter 40gr bullet out to 200 yds. A fraction of an inch of accuracy can mean a target on the ground or frustration. The goal is to put all of the prone-shot targets on the ground, then hit as many chickens as possible. The top shooters will go all out in terms of barrel (requiring a match chamber & crown), best lot of  real  match-grade ammo, best sights/scope, and fit (weight, length of pull) and balance of the rifle. Measuring rim thickness or weight-sorting ammo can also be part of the process of getting to ultimate accuracy in your rifle. Whether or not measuring rim thickness works for your particular rifle and ammo will be proven by testing on paper. The proof is on your target, not necessarily by what someone else's experience is. Then after all this, a sudden gust of wind or mirage shift can make the most accurate rifle a victim of conditions......