Sort Ammo by Rim Thickness, Reduce Flyers

Zee705

Zee705

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I picked a Raven Eye Custom rim thickness gauge from https://www.canadiangunnutz.com/forum/member.php/141849-TheWhole9Yards recently and I wanted to see if I could get a bit more consistency out of different kinds of ammo. The theory is that rim thickness will vary between rounds which means that the amount of primer compound varies affecting velocity. I'm basically looking to reduce flyers.

My first test will be with CCI SV at 50 yards then I'll move on to SK RM.

The gauge can be used with either a dial indicator or calipers. I have an indicator but the quality of it is suspect and I saw better repeatability with the calipers.

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After sorting 170 rounds I found the following:

0.0400" - 1
0.0405" - 10
0.0410" - 44
0.0415" - 64
0.0420" - 44
0.0425" - 6
0.0430" - 1

The Test

The test rifle will be a Bergara B14R Carbon at 50 yards. I'll shoot a group of 5 random rounds from an unopened box, then shoot a group of 5 of the same rim thickness from the sorted ammo and continue like that until rounds complete. When I'm nearly through all the sorted rounds I'll shoot a group 5 different thicknesses, this should theoretically be the worst group. The average group size of the sorted rounds should be smaller than the random rounds.

Any suggestions or comments about my experiment?

If you're performing a similar test, post your results.

Cheers
 
I had an old Champions Choice catalogue and was reading it in a car pool. I remember one of those Ah Ha exclamations when I realized sorting for rim thickness was a thing. And I just thought you bought more and more expensive brands.
 
5 round groups, especially the randomly selected control group, are not big enough. My experience with CCI SV, maybe 4K worth in a T1X, is that 10 rnd groups are where you start to see the variability of the ammo. Shots 7-9 really open things up often. Benched in an MDT ACC chassis with a StrikeEagle at 50 and 89M is how I shoot groups. Other than that, I’m really curious to see your results. If I can save 40-60% in ammo costs by sorting, that would be great.
 
I have a Bald Eagle and Eley Match is within 0.001"
Separating them into two groups is about the best that could be done.
A standard measurement might be around 0.037" so the two groups are less than and greater than 0.037".
Having test both in my Remington 40XB I would be hard pressed to tell the difference.
Six 10-shot groups for score averaged 0.77" under great conditions and over wind flags.

The statistics from the original post . . .

0.0410" - 44
0.0415" - 64
0.0420" - 44

. . . suggests three groups to test. Wouldn't it me a shame if that group of 10 proved to be better but hopefully you find those in the middle work best.
Otherwise you have a lot of practice ammo.
 
I have a couple of rimfire rifles that like Federal Champion which I buy in the 525 round value pack. I have found that the batching of the rounds by rim thickness brings in the accuracy slightly, but really reduces the number of flyers experienced. It's a worthwhile exercise, particularly for the cheaper bulk packs. I did the same exercise on a couple of packs of expensive match rounds, waste of time, there was too little variance to batch them.

Weighing them is the next exercise, will be interesting to see if there is much difference there too.

Candocad.
 
I don't see the statistical merit in splitting the sorting in only two groups. You have half the dispersion of a wider sample, but the weighting is hard skewed towards that 37 measurement without eliminating the extremity. Weighing might be an option within a measured sample, but the spread is probably going to be very small. If anything weigh and arrange in order. But start light and go heavy or vice versa?
 
Hi Zee705,
Awesome that are are going to test this. We have all experienced the bizarreness of strange fliers that wreck an otherwise tight group or which ruin our score on a competition target. There is tons of discussion on various forums about rim thickness with a wide variety of opinions. I have attempted to test rim thickness, but failed for various reasons. (wind is one of the un-controllable variables where I shoot, which confounds results). I look forward to seeing your results.

For your experimental design, I think you can eliminate the random unsorted groups because they don't tell you anything relative to the variable you are testing which is rim thickness. Instead compare sorted rim thickness groups to each other, and this will provide the evidence, or not, that rim thickness is correlated with fliers or coarse group size.

A note about weight: I have weighed several hundred rounds of SK Match, and found a weight range of 51.00gr to 52.00gr, (one grain), which is a variance of roughly 2%. Its unknown of course how this is distributed between bullet, brass, powder and primer. I have attempted to test precision by weight, but again failed due to several uncontrollable variables, including me the shooter.
 
It's good to be doing this experimentation, but would be better to post with results rather than speculating.
 
I ran into a guy sorting ammo like this at the range, when I saw his test gun was a stock 10-22, I chuckled and walked away.
I have been told by serious competitors it make a difference.
 
The amount of primer should not change what ever the thickness of the rim. The machine that drops the primer always drops the same quantity. But maybe it changes the way it spreads in the casing. Am i wrong?
 
dugasgunner said:
The amount of primer should not change what ever the thickness of the rim. The machine that drops the primer always drops the same quantity. But maybe it changes the way it spreads in the casing. Am i wrong?
Click to expand...

As far as I know federal and CCI ammunition is hand primed using a large scraper over the cases, kinda looks like they’re applying mud to drywall. Not sure if that is more or less accurate than a machine.
 
Are 22 cases machined or cast? If the later, weight issues will be from that. Lead casting is going to be pretty darn consistent, especially if you believe that all the rounds in your box are going to be sequentially dropped off the conveyor.

Curious if this changes anything. Is 25y indoors too small to tell?
I remember when i first started weighing my pellets, nowTHAT is obviously worthwhile!
 
Jahnj0584 said:
Are 22 cases machined or cast? If the later, weight issues will be from that. Lead casting is going to be pretty darn consistent, especially if you believe that all the rounds in your box are going to be sequentially dropped off the conveyor.

Curious if this changes anything. Is 25y indoors too small to tell?
I remember when i first started weighing my pellets, nowTHAT is obviously worthwhile!
Click to expand...

I'm fairly certain that all brass cases are 'drawn' from a pellet to final form. Usually they are annealed after the drawing process, though probably the 22lr cases are not. There's various videos out there on how ammunition is made, some of which show enough detail on the brass production to glean answers.
 
TheWhole9Yards said:
As far as I know federal and CCI ammunition is hand primed using a large scraper over the cases, kinda looks like they’re applying mud to drywall. Not sure if that is more or less accurate than a machine.
Click to expand...

CCI and Federal apply the priming by hand to all the .22LR rounds they make each day? That would be something to see.

For the general reader, some basic information on how .22LR ammunition is made can be found in this article https://www.americanrifleman.org/articles/2017/8/16/what-you-should-know-about-22-rimfire/
 
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