22lr Rim Thickness

[ppkny]

Has anyone did any rim thickness measuring? I bought a rim thickness gauge and started to sort my SK Standard and SK Match Ammo. I wondering if it's really worth the trouble. I checked 3 boxes of each and the biggest variation I got was .0015. Most are within .0000 to .0005 of a measured lot through all boxes.
What's the normal? I've never done this before and don't no what to expect.
ppkny

[Doodaddy]

If I were to measure any one thing on rimfire ammo, it would be from the top of the rim to the leading edge of the driving band.

Measuring only rim thickness ignores important details like where the variation in the rim thickness is in relation to overall brass length as well ignoring bullet seating depth. Who cares how consistent the rim thickness is if your bullet depth is all over the place.

Measuring from the top of the rim to the driving band of the bullet will enable you to be consistent in bullet placement when chambered; whether it's how much of a jump you have or how much contact with the lands there will be, because then the variations of the brass length or rim thickness won't matter in the grand scheme of things. You know the key metric is where the bullet is in that barrel. Measuring in this manner will show that rim thickness varies outside of the chamber and could possibly impact ignition by being farther from the barrel and being striked by the firing pin sooner, but I doubt it would be enough to ever be measurable in performance or possibly even lock time.

Recording rim thickness or OAL or weight or most any single measurement on rimfire ammo ignores too many other aspects of the cartridge you would also have to measure to provide context to your original measurement.

If the rim thickness varies...ok...what does that variation impact? Did the location of the leading edge change? Was the the base that changed? Was it both? Something else you'd have to measure.

Weight changes...ok...was is brass density? Lead density? Power variation? Primer variation? Lube amount? Who knows if you can't measure it all separately.

OAL varies....ok...so the tip of the bullet isn't in the riflings so you'll have to see where the driving band is in relation to the bullet tip and what if the rim thickness isn't consistent so you'll measure rim thickness to see where the variation is OAL is.

Trying to control the variables in factory loaded ammunition is a rabbit hole you don't really come out of because you would have to disassemble each round to properly find the individual measurements that we can and do with hand loaded centerfire ammo.

In the game of silhouette, I personally think what accuracy improvements that can be gleaned from measuring ammo (outside of lot testing) isn't really score impacting so I don't currently measure anything because like you asked, I don't think it's worth the trouble. That and I think the ammo Lapua/SK/Eley is producing these days is great and doesn't require such tedious activities. Maybe if you're trying to get all you can from some cheap ammo you just want to burn up, but if I were to measure anything, it would be the leading edge of the rim to the leading edge of the driving band to ensure the bullet is seating consistently.

[ppkny]

DoDaddy,
Thank you very much for your thorough explanation of the dynamics in what it takes to make a precision bullet/cartridge assembly. You are spot on. In regards to 22LR ammo your statement:

DoDaddy wrote::Measuring from the top of the rim to the driving band of the bullet will enable you to be consistent in bullet placement when chambered; whether it's how much of a jump you have or how much contact with the lands there will be, because then the variations of the brass length or rim thickness won't matter in the grand scheme of things. You know the key metric is where the bullet is in that barrel.

This seems to be a key factor in all reloading along with all the other variables. The theory behind the rim thickness check, as I've read, is to make sure all bullets SEAT the same way in the chamber when the bolt is closed regardless on where they are in relationship to the lands. Granted where the driving band is in relation to the bullet tip is the ideal dimension check.

I do hand load for my 6.5, 260, 30-30 and 357 guns so I am familiar with most loading procedures in controlling these variables but with 22LR the manufacture has the control. I should have mentioned that I was also weighing the cartridges but is it the bullet, powder charge or the brass that is the variable?

I also should mention that this is for 22LR Mini Palma rifle not silhouette. So other than buying Eley - Benchrest, Tenex or Match at $120/$190 a brick I'm trying to get the best performance out of my SK & SK Match ammo.

I think I can modify my gauge to check what the driving band is in relation to the bullet tip in your illustration so I'll give it a try.
Again, Thanks a lot for your help.
ppkny

[Doodaddy]

The theory behind the rim thickness check, as I've read, is to make sure all bullets SEAT the same way in the chamber when the bolt is closed regardless on where they are in relationship to the lands. Granted where the driving band is in relation to the bullet tip is the ideal dimension check.

That's why I went through so much detail because the theory behind rim thickness checking is flawed.

Let's say for instance one rim is significantly thicker than the other 45,000 rounds you checked. Does that mean it will seat differently? No, it means you have to measure other aspects of that round to give any sort of value to the rim thickness. If the body length of the brass of the brass changed due to the rim thickness, then yes, it will seat differently.

But what if the body length of the brass doesn't change and the rim thickness is 30% thicker. How does that change the bullet seating in the chamber? It doesn't, because that thickness variation didn't impact anything that entered the chamber. That's why I was talking about the leading edge (probably poor terminology...the bullet side of the rim) and the base of the rim (the opposite side). If the rim thickness varies from "perfect", one of those edge's location has changed in relation to the rest of the cartridge. If it is the non bullet side of the base, who cares? If it's the bullet side of the base, that could change bullet seating, but you won't know which of the two is occurring without measuring something else. Even then, you've found the variation in the brass, but no relation of that to the bullet so you're off to measure something else.

Which is why I say measuring rim thickness on its own an effort of futility. Measuring from the top of the rim to the leading edge of the driving band will do exactly what you're wanting: consistent chambering. It accounts for the relationship of that leading edge of the rim and the first part of the bullet to touch the lands. You won't know the variations between those two points, but you also won't need to because they all worked together for your final goal.

I also should mention that this is for 22LR Mini Palma rifle not silhouette. So other than buying Eley - Benchrest, Tenex or Match at $120/$190 a brick I'm trying to get the best performance out of my SK & SK Match ammo.

I think I can modify my gauge to check what the driving band is in relation to the bullet tip in your illustration so I'll give it a try.

That makes plenty sense. Now to play devil's advocate.

How are you going to measure the ammo without deforming the lead or disturbing the lube on the bullet? Since you're shooting SK, you'll be better off with their oil film than Eley because you'll never get an accurate measurement on Eley involving the bullet unless you wipe off that thick wax effectively ruining it. If the lube or bullet shape is impacted, you introduced a new variation chasing down the elimination of another.

Food for thought.

[Sporty]

I did considerable testing of variable rim thicknesses and sorted the rounds by +/- 0.0005" groups. That means one group will contain 0.0385" to 0.0395" rims. The reason I did all that work was because the 5000 round case of .22 LR Eley CMP SV ammo rims varied from 0.034" to 0.045". 80% of the case was 0.039" +/-0.0005".

One of my rifles tested is an old Mossberg 46B. You can imagine that rifle wasn't built to tight tolerances. From the bench rest, that Mossberg has its tightest group with the 0.035" +/-0.0005" rims. Unfortunately, I only found about 150 0.035" rounds in that 5000 round case.

I found match grade ammo in the Lapua CenterX and higher grade and Eley Tenex had very tight variations, or none at all, in rim thickness. Lapua is relatively thicker than Eley. Consequently the point of impact at 100 yards varied between the two but I can't tell you if it was because of the different rim thickness.

In other words, match grade ammo is so consistent that sorting by rim thickness isn't necessary.

[_Shorty]

edit2: 2022?! Oh man, this forum is dead. hahaha

Sorting by weight helps. Doesn't matter whether or not you know why it weighs a different amount than the next round does. Rounds that all weigh the same will naturally be more similar / have less variations than rounds that have a lot of different weights. Even if the reason they weigh differing amounts is unknown to you. I'll never understand people who insist that because you don't know what makes them weigh a different amount that you then have no reason to bother. Doesn't work that way. Reducing variation reduces variation. (The difference is in the bullets anyway. Nothing else weighs enough to account for the deltas. I've disassembled way more rounds to weigh individual components than anyone ever should. Hehe.) Sort them by weight and use the majority bin for turkeys and rams. Save the smaller bins for chickens and practice.

Sorting by rim thickness helps. (Olympic athletes have done this one in the past, and may or may not still do so today. I occasionally shoot with one who volunteered this info one day out of the blue.) The theory is this helps get better ignition consistency due to having more consistent brass thickness. Whether that's the actual reason or not doesn't really matter. All that matters is the process results in better performance on target, just as sorting by weight does. And, again, it doesn't matter whether or not you know why the thickness differs. If you reduce variation, you reduce variation. Variation will still exist, just as it will still exist when weight-sorted. But you're making all the examples in the majority bins more alike than when they're randomly among the rest of the population. The variation reason will still be unknown, but you've made the amount of variation smaller, regardless. And thus, the rounds will also behave more alike. And again, save the majority bin for turkeys and rams. Save the smaller bins for chickens and practice.

And the process you mention, sorting by rim to driveband, also helps. I built a tool with a dial indicator similar to one that someone used to sell, who as far as I can tell may no longer make and sell, to sort via this method. Just like the other sorting methods, it does indeed give you tighter groups. I wouldn't say it is better or worse than the other two methods, though. There doesn't seem to be a clear winning method.

Is it worth your time? It isn't going to make the lowest tier target ammo shoot like the highest tier target ammo. It will give you better results. How much better? Not earth-shattering, but noticeable and quantifiable. Which method is better? Depends on the ammo you're starting with, and you'll have to try each method with that ammo to find out. Even Eley Tenex varies, sometimes by a surprising amount, in all three methods. Same for Lapua's expensive stuff. If you're lucky you can take something like Eley Sport/Target and make it shoot about as well as Eley Club.

Can you get even better results by combining some or all of the sorting methods? Yeah, but you're quickly culling more and more ammo, and pretty soon your remaining bins begin getting rather small. And you'll spend more time than the price difference, even just sorting via a single method. Whether or not you mind spending that time is an individual thing. Everyone's time is worth a different amount to themselves. And after sorting you can also dive into the Neal Waltz die if you like. It helps, too. It never ends. haha

edit: And don't forget, all this sorting is culling rounds, thus making your remaining rounds more expensive, in a way. If you buy a case of Eley Sport for $750 or whatever, let's just say $750, then each round is $750/5000 15 cents. But if sorting by weight removes 20% of them from your "I want to shoot these in a match" pile, well, the 4000 remaining rounds basically cost you 18.75 cents each now. And maybe it would only cost you 17.5 cents a round to buy Eley Club instead. So, it works. But is it worth it? All depends on how you look at things.

[PAndy]

We have measured rim thickness to compare different brands of ammo. Eley seems to consistently have thinner rims than other brands. I believe it was contributing to light primer strikes in a marlin 39a rifle.

I have never messed with it for accuracy sorting.

[_Shorty]

We have measured rim thickness to compare different brands of ammo. Eley seems to consistently have thinner rims than other brands. I believe it was contributing to light primer strikes in a marlin 39a rifle.

I have never messed with it for accuracy sorting.

Yeah, standard headspace for 22 LR is 0.043", and Eley's product literature suggests using a headspace of 0.041" with Match and Tenex.

[375Short]

My SB Rifle shoots a number of Eley products well but is unusable in a match due to failures to fire. The thin rims or my rifles headspace being the culprit (same end result). If having a RF rifle built or re barreled I will set it up to Eley thin rim headspace in the future. This won’t preclude using RWS or Lapua cases but headspace on the generous side for the R or L brand makes the E brand sporadic to fire. I see only disadvantage to excluding the ability to use a significant brand option. Every factory Anschutz I have had ignites Eley and other brands fine. CZ / Bruno rifles can go either way but with the 455 / 457 not a hard problem to solve. With lever guns I have the same problem as PAndy they typically are generous on head space. If you have a lever gun like a 66 or 73 the strength / thickness of the brass also matters during ejection. Eley is thin and frail, Lapua / SK / CCI / Federal not bad at medium and RWS / Norma / GECO hard as a rock by .22 brass standards. The thin and frail can cause a jam by squeezing back into the loading block / lifter instead of being pushed out the top causing a stress inducing jam. This seems to occur more often at a match instead of during practice just to make sure you get full value from the experience.

[Grantmac]

If I do another customer rimfire it'll be a coned breach and threaded with a barrel nut.

[_Shorty]

If I do another customer rimfire it'll be a coned breach and threaded with a barrel nut.

Bolt shims are another way to approach the issue. https://www.triggershims.com

[375Short]

Barrel nut is a great way to go. Allows for adjustment and ideal for changing one’s mind on barrel configuration or the ability to switch back and forth. One silhouette barrel and one light field weight barrel for hunting. Options.