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 (You need to Login or Register to view media files and links)

Wayne

Years ago I wasted a lot of time sorting with a Neil Jones rim-thickness gauge.  Can't remember exact results, but my final conclusion was...not worth the trouble.

In the past I shot a lot of handgun silhouette. Two NRA national championships and many state championships. I went through the measuring & weighing stages and came to the conclusion that neither were worth the time.

Boats, very good points.
I shoot .22 BPCR Silhouette, targets are at 50, 100, 150, and 200 meters. MOA accuracy is pretty much minimum so using anything less than top-quality ammo is a crap shoot at best. Finding the ammo that your rifle likes best , as well as the best lot of that ammo, is pretty much like load development in a big bore BP rifle. When it comes to ammo, old Chinese proverb comes to mind - "you pay peanuts and you get monkeys".

I'm with Boats.  It costs me $12 in gasoline for a round trip to the range, plus match fees ($5) plus membership.  All sunk cost before you fire the first shot.  All you really require is that the ammo shoots better than you.  But you don't need Tenex for offhand unless you are really good.

Also, is the expensive stuff always better?  Last Sunday I won a BR-50/50 match by 6 points.  I used new Midas + and got 8 hits on the X-dot.  Second place used Wolf Match Extra but had 18 hits on the X-dot.  I shot an Eric Johnson Ballard with a 12X Unertl.  David had a BSA International Mk II with a modern scope of some sort, 24X.

Tuesday (yesterday) the Tuesday Afternoon Schuetzen Verein had a 100-yard rimfire bench match using the ASSRA targets, two 25-shot targets.  The range is on the left coast, about 300 yards from the surf, and faces SW.  Wind, glare & some sort of mirage or mist are given.  Same rifle & ammo for me, I won with a 1204-20 centers.   

Second was a guy who has only been shooting for two years and hasn't much $$.  He used a Remington 513T with a modern 10X scope and Wolf Match Extra.  He had 1198 points and 16 centers.  After that, I have my doubts about the Midas +.  I tried two 10-shot targets at 100 yards; 245 with 4 centers and 247 with 7 centers.   

Another shooter at the Tuesday match used a Stevens Crackshot with a Win 52 barrel and a 30X plus modern scope.  He shot CCI High Velocity ammo.  Score was 1173 with 17 centers.

All that is out of the box.  I have weighed 22s, but you have to go through at least 1,000 to be able to find a really stable batch.

I agree with John, I quite rim thickness years ago after I found the inconsistency of the measurement (rotation issue) and frankly lack of cause and affect from variation. I strictly weight now. That said I have a friend who shoots IRA and ARA bench who measures weight and over all length and swears he has had great results.

.22Hepburn wrote on May 17^th, 2018 at 11:02am:


My understanding is uniform ignition & accuracy, is effective by how well the primer compound is ignited, which is directly related to the impact of the firing pin.  Variations in rim thicknesses affect the firing pin strike & therefore affects ignition.  I have recently had direct experience with marginal .22RF firing pin strikes due to a worn & disfigured firing pit tip.  The result was flyers, even with high-quality ammo.  Replacing the firing pin solved the problem.  A variation in firing pin strike also affects center-fire firearms.  An example is the well-known results with Sharps rifles when, unknown to the shooter, the firing pin breaks.  The broken pin still has sufficient energy to fire the cartridge but unexpected flyers result.

With the above said, and due to my recent testing of .22RF ammo with the rim thickness gauge, I agree with the comments made that rim thickness testing is a waste of time with high-quality target ammo.  The gauge may have a use when sorting economy ammo to use for target shooting.

Concerning different actions, I'm no expert but I'd expect headspace to be much more important than how tightly the block cams or locks up. But headspace won't fix variations in rim thicknesses.

Wayne

texasmac wrote on May 17^th, 2018 at 12:51pm:


Vickery's Advanced Gunsmithing devotes a page of illustrations of different firing pin strikes on case rims, with explanations of the effects of each on ignition.