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Old 02-25-2017, 01:25 PM   #1
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40SW case variation

I did a random weight check on my 40SW brass (assorted headstamps). It was cleaned and unprimed--just the brass. I checked the case length and they were all the same, but as much as 10.5 grains weight difference!!! Is that too much? I don't usually sort handgun brass, but should I?
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Old 02-25-2017, 02:16 PM   #2
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I would not be concerned about the weight difference in various brands of brass cases. Many of us shoot range pickup/multiple brand brass with no problems. IF you are shooting bullseye 50 yard competition, then I would stick with one brand of brass, plus many other considerations. If you are a range shooter like many of us......load it up and enjoy!!!
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Old 02-25-2017, 09:20 PM   #3
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I'm not as concerned about the lack of weight uniformity. I doubt there are many, if any, people who could tell the difference in accuracy with a hand-held firearm at normal pistol distances with the kinds of deviations I'm talking about here. I'm not talking about bench-rest accuracy.

My concern is not the presence of the weight/capacity deviation, but the amount of deviation-- well over 10%. I don't know how much a % of change in case capacity affects pressures, only that it most certainly does. All reputable manuals advise reloaders of semi- or full-auto firearms to make sure the ammunition does not allow for bullet setback for this very reason.

My concern is about the safety of the ammo, because the weight is a factor in determining case capacity, and therefore pressure, and therefore safety.

If you change your powder charge by that amount, you can very quickly go from safe to unsafe (or vice versa) pressures. It's also my understanding that, because of the nature of smokeless propellants, the pressure curve can rise exponentially rather than linearly at unsuitable pressure levels (high or low).
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Old 02-26-2017, 01:53 PM   #4
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Your concern is valid particularly if you are loading at or near max. The difference in case wall thickness, since it obviously means the inside diameter would be smaller and, as a result case volume would be reduced; or that the case base is thicker with the same result, would translate to higher chamber pressures.

That said, perhaps the easiest solution might be to reduce your powder load from max to max minus 10%.

I personally sort my cases by manufacturer before reloading them. I also check my fired cases for flattened primers before cleaning them. Flattened primers are a reasonable indicator of excessive chamber pressure.

There is also a possibility of having unburnt powder left in the case if the case volume is reduced and there isn't sufficient space even if pressures are not excessive.

Last edited by abninftr; 02-26-2017 at 01:56 PM. Reason: Added thought.
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Old 02-26-2017, 02:10 PM   #5
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A 10 grain difference isn't a lot when you consider how small a grain is... 1/7000 of a pound...

Maybe it would make a difference at absolute max loads, but I don't load as hot as possible anyway... fact is the hottest possible load is seldom the most accurate load...

10% below max is likely to be a good load for most shooting.


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Old 02-28-2017, 09:34 AM   #6
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Gee, is your worry was important, the reloading manuals would cover weighing and sorting the cases.
You are confusing the games that precision long-range rifle shooters use, generally without any verification that it matters and is just a "consistency always improves accuracy" justification, with a gun that is lucky to shoot 12 MOA. I find .40S&w is more temperamental than other cartridges, but find no difference in mixed cases.
Read and follow the directions in the loading manual and stop looking for non-existent problems.
Otherwise, just live with sorting all cases by weight and loading, if that will make you feel better.
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