Rimfire concentricity,weight and rim thickness

P

Pieter.45

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Hello all,

I was wondering:if it makes sense to weigh cartridges and measure their rim,is it important to measure the concentricity of the bullet in the case?Or is it rare they run out(quality ammo like eley match)?
I'v just weighed a batch of eley match and there was a little difference,but no extremes.Most were between 50.9 and 51.1 grains (50%) and some were between 51.2 and 51.5 grains (35%).The others were below or above that and these will be used for training.
As to measuring the rim,I'm still waiting for my tool to arrive,but how much difference is acceptable?
The same goes for the concentricity:how much is allowed?
By weighing the ammo,is it the way to go like this or should I devide them by 0.1 grain instead of 0,3 grain.
All help is appreciated as I'm quite new to the benchrest scene.

Greetings Pieter
 
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I have done neither but those that have, have, for the most part, found no correlation between weight and rimthickness to accuracy in quality ammo. When you weigh, the difference could be in the bullet, the powder, or the case. You can not issolate the components. Rimthickness is pretty consistent with quality ammo and runout, according to Calfee is corrected in a match chamber.
 
Ah...so all this makes no sense.
It's ok to stick with match ammo which doesn't have these problems.
As to weighing of course you don't know what causes the difference.
 
Coincetricity is controversial somewhat. I tend to believe in it and have found the better lots of ammo tend to have less runout, I suspect crimp is at play here.
 
I weighed a whole brick of SK Pistol Match, and I found a range of variation from 51.3 to 52.3. Now some may say that this would make no difference, but I find it strange that the heavier ammo I grouped together seemed to shoot better than the lighter ones. Also I would bet the black or red box Eley will not have that much variation. Probably another reason the Eley ammo is just a little more consitent with fewer fliers. I can't say sorting makes a real difference, but I do know that it is boring to do a whole brick at a time. I gave up on it. I think your better off buying the better ammo if you can afford it.
 
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I did this some 10-15 years ago and found the best ammo of the day, Eley BRG (Cera 1995) made no difference. But with cheaper ammo it did make a difference. But the cheap stuff didn't shoot as good as BRG. Since the lead bullet is by far the heaviest component I would guess it is the component detected as varying. The powder its self doesn't weigh but .7 g (again my memory) and enough variation in it to cause problems probably won't show on most electronic scales. Priming could cause major problems but again I don't think ordinary electronic scales would detect it as if the lead varied .1 you wouldn't detect it.
 
So it only makes sense in the cheaper ammo then.
I used to shoot sk standard plus and it grouped really well but in one box I had about 5 flyers.
Now I shoot eley match and it's rare I have flyers.In practice so be it but in a match you don't want that.So I was thinking to check for rim and concentricity on my match ammo.
 
More food for thought . . .

About 5 or 6 years ago on this rimfire forum, there was a discussion on weighing, and guesses were made on which component have the greatest variance. I'm retired and have lots of time on my hands. So I weighed three bricks of Wolf Match Extra.

I filed my notes away on that little test - Somewhere . . . A couple of days ago while reading this thread I remembered those notes. Now where in the hell did I put those notes? Found them tonight.

Anyway: I weighing 1500 Wolf Match Extra cartridges. I had an extreme spread that went from 39.4 to 40.6 grains: 1.2 grams. That is not as good as the test run by Brad on a brick of SK Pistol Match. He got an average of .9 in his test.

I set aside the 10 lightest and 10 heaviest rounds. Those other 1480 rounds had an extreme spread of 1.0 grains. Not bad: I have weighed a few boxes of Eley Black Box with a spread of .80 grains.

So: What I did next was to pull the bullets from 5 of the lightest rounds and 5 from the heaviest. I weighted each bullet.

The average weight of the light bullets was 39.71 grains
The average weight of the heavy bullets was 40.54 grains.
That is a variation of .83 grains.

Then I cleaned off the lub with carburetor cleaner and weighed them again.
The average weight of the lub (as close as I could measure it) was .06 gram.
I have two scales that are claimed to have an accuracy of + or - .1 grain. The scale uses in this test claimed to have + or - .05 grain accuracy.

I weighted the powder and then the cases with the primers still active. The brass and the powder variations were so small, I could not measure them with that scale.

My questions at that time were: Will a bullet that weighs .83 grams lighter than another have a higher velocity? Will the weight difference cause a different barrel vibration pattern? Will the bullets exit the muzzle at different point in the muzzle movement?

I think the answer to the first question is no. I checked the JBM ballistics calculator on-line and the two bullet weights gave the same velocity.

I leave the 2nd and 3rd questions for some of you to answer for me.

Brad found that the heavier bullets seemed to shoot better than the lighter ones. Makes sense to me: There can be inclusions of other elements in the lead. They would be lighter than the lead. The more inclusions, the lighter the bullet. If the inclusions are "off-center": Could that weight difference cause the spinning bullet to be unbalanced?

Joe Haller (Mr. Frosty)
 
Actually Joe after looking at one of the groups I just found out that the heavier rounds from this sorted ammo was 52.3grs. So that is a variation of 1grs.

My buddy tells me if you weigh ammo the ones that weigh the heaviest will be due to the fact that it only makes sense to him that the bullets from these heavier rounds will have less porosity or air bubbles inside the bullet. Makes sense to me. He said that the lighter ones probably will be more sporadic and have a tendency to produce your fliers. Now he said that to me after I told him my results. He said it makes sense to him, and I guess was thinking out loud or telling me his theory on this. I do know Don is one smart cookie. Now I am not saying that this is proof that this is the way it is. But you do have to wonder from my results that Don may just be right.

That same SK Pistol Match ammo that I weighed, I played around with tuner weights shooting the 21oz total tuner weight(that's the regular 8oz Hoehn tuner with a 8oz weight screwed in next followed by a 5oz weight on top of it), and this ammo was shooting holes. I shot this one and some more that were below .150ctc I believe. I then shot a 242 USBR I believe with the same ammo. Not too shabby at my range. This group was shot with a box that weighed 52.3-51.8grs.

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Here's a few more I shot from that same ammo I sorted that were the heavier ones.

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I honestly don't think this was a coincidence. I also shot 2 more back to back 10 shot groups that were under .300ctc which is pretty good for 10 shot groups.

I subtracted .204 for bullet diameter on all these groups. So if you want to subtract .224, take .020 more off of each.

I can honestly say that the lighter ones out of this same brick didn't shoot as consistent as the heavier ones.
 
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This theory has 2 camps:believers and non believers.
I recon myself to the first.
How can you have utmost accuracy with different bullit weights,even minimal.
Concerning the eley match I've weighed 4 bricks now and I had no more than .8 grs difference neither.
And with cheaper ammo I've had more diffference too.
So like I presumed,top notch ammo has less difference.But there still is difference.
I don't know but I presume this goes for the rim thickness too?I am about to receive my gauge(normally next week) so I will find out soon.
I was seriously thinking of measuring and weighing the ammo I will be using in a match.
 
20 to 30 years ago rim thickness was a much bigger issue. In those days we used Win and Rem. "target" ammo for practce and the thickness spread could be great. Even Eley had to be checked. Todays Eley the spread is small, BUT in every box I have checked there seems to be one or two "skinney" ones. Sooo in order to go to a big match with your head screwed on straight it pays to throw out all ammo out of range. That way all fliers belong to you, or maybe it was your scope.

One of these days I'll run the oddballs both rim thickness and weight through my CHRONY.
 
Seems I always remember the bad shots. Two years ago at a tournament at Mill Creek I had a dud on the 23rd shot of the 6th and last target. It had a noticeable milder sound and hit low for a zero. Would weighing have detected it? I don't know. From the sound I would guess it was short on powder. If no powder at all, the primer I don't think would have got it to the target 50 yards away. Might have even stuck in the barrel. Maybe xray would help.

Last night at a indoor 3p match I had a round that would not chamber in my Martini. I sat it aside in the loading tray and checked it later. The bullet was not fully seated in the case and was cocked. I think I paid about .18 cents for that round.:rolleyes: I wonder if I can sell it on ebay. Rich
 
Weighing bullets

Back around 1982/1984 when I was on a real budget trying to raise children and have a little money to shoot too I weighed my ammo that I shot in 22 silhouettes. I was shooting Winchester super-X and having good luck with that system. These were copper wash bullets and they wieghted about the same.The nominal weight was 51.8 grs and back then they seemed to shoot lites out. I have some left now and they won't shoot for a hill of beans. Back then we shot open sights (I could see back then) and in my teeny little mind they seem to shoot great.
We didn't check the rim thickness back then or at least I didn't read about it anywhere. Now the older I get the less time I seem to have so I just buy better ammo and spend that time shooting.
MHO
Larry
 
Just for a minute, ignore your stance on sorting, by any means, weight, rims, whatever. Ignore the fact that you think it might/does work, or, ignore the fact that you think it doesn't/can't work. Just for one minute, you have no stance on sorting, good or bad. And for that minute, consider the following.

Let's say I have two rounds:

Round 1: 51.7 grains
Round 2: 50.8 grains

What are the chances that both cases weigh the same? What are the chances the primer in both weigh the same? What are the chances both powder charges weigh the same? What are the chances both bullets weigh the same? I think the most important question is, what are the chances that those two complete rounds are the same? Can you honestly answer anything other than absolutely zero chance?

Now, let's say I have two more rounds:

Round 3: 51.3 grains
Round 4: 51.3 grains

What are the chances that both cases/primer/powder charges/bullets weigh the same? What are the chances that those two complete rounds are the same? Not 100%, but definitely not zero, right?

Any chance better than zero is most definitely better than a guaranteed exactly-zero chance, wouldn't you agree? You have no way of knowing where the difference lies between a round that weighs 51.7 grains and one that weighs 50.8 grains, there's absolutely no debate there. 51.7 grains is different than 50.8 grains, period. There are several components that could be different. Any one, or all, of them could differ in each round. No matter which component or components are responsible for the difference, the difference is there. The chances of two rounds that both weigh 51.3 grains being similar and performing similarly has certainly got to be higher than two rounds with vastly different weights performing similarly.

Manufacturing tolerances of individual components, and assembly tolerences of all components being added together, obviously vary, and vary enough to combine into rounds that are measurably different. If they weigh different amounts, you are guaranteed that they are different, no matter where the difference lies. They have different weights, so they absolutely do differ in one or more ways. If they weigh the same, you're not guaranteed that they're the same and will perform the same. But the chances of them being/performing the same are much better than ones that are guaranteed to be different.
 
No brainer

Really, if you think sorting will help you in some way, it will! Mental attitude is huge. I get better times out of high school x-country skiers by using "secret" waxes and voo-doo stuff. Some might work for a hundred yards, some are pure head games. When interviewed at the end of a race they all rave about coaches "special" wax,etc.. Demoralizes the opponents and makes me a guru of sorts. Bottom line: They think they're fast, they're fast. Buy the highest quality ammo, sort it to what ever level you think is best, go into the match with no ammo worries. How can that be anything but good? Also kills time when it is below zero in the Great North! Good shooting, Guy
 
Excellent point! At the same time, I don't think mental attitude has much to do with 50.8 vs. 51.7 & 51.3 vs. 51.3, do you? Even if you don't think it will make any noticable difference in where they hit the target, is it really that much of a stretch to think that two rounds that are 51.3 grains and 51.3 grains are probably much more alike than two rounds that are 50.8 grains and 51.7 grains? I'd sincerely like an honest answer to that simple question.
 
I don't get it.
I've checked a batch Eley match.There were a lot of differences in concentricity.About half had more than 3/100 mm runout.You can actually see the worst bullets wobble in the concentricity gauge.
So I checked the Lapua Center-X out which I still had.These were much more consistent:almost no runout,only 0.3grs difference in weight and a more uniform rim...
So sorting has impact?Yes and no_On the Eley you get a bit better groups on sorting the ammo.With the Lapua I noticed no gains.
It all depends on the quality you start with.I find it strange Eley is "inferior" in consistency compared to Lapua.But sorted Eley outshoots Lapua in my case.
 
Sorting

So by buying high quality ammo and sorting it you found some that shoots well and are at ease with the performance potential of your ammo?
 
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Well yes.But you gain little with a lot of work.It's all in the game I guess.
 
One of the reasons that I am into rimfire is that I do not have to mess with weighing and loading ammo.

I buy the better stuff and my life is simpler.

If you want to reason out where the variation in weigh is consider this:
If the loaded round weights 50 grains and the bullet weighs 40 grains the bullet is 80% of the weight so it is likely that it will have the most variation.

If the amount of powder is 1 grain in most of the cases and one has 1.1 grains of powder then it an increase of 10% and almost no weight at all.

This stuff will drive you crazy if you let it. You may become a basket case.

Concho Bill
 
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