Case Weight Differences?

[SgtMajor]

Does anyone have knowledge about loading cartridges with different case weights? I find 4 to 6 grains weight difference in the same brand cases & I'm wondering how much this affects the performance...... should powder weight be adjusted to compensate? I have not found any case weight data in any loading manuals.

Thanks everyone.....

 

[taliv]

i can't tell you how much it affects performance. I guess that would depend on what sort of performance you're looking for.

I can give you an example of one of my precision loads. This is for the 6xc caliber using Norma brass.

I bought 300 rnds of it and found the average weight of a large sample (probably around 25 cases chosen at random) was 158.17g with a stddev of .47g

I found many of the cases fell into groups, so I made 3 "lots" of brass.

lot 1:
avg weight 157.99g
stddevp .07g
max weight 158.08g
min weight 157.88g

lot 2
max weight 158.48
min weight 158.26

lot 3
max weight 158.69
min weight 158.49

so basically, cases in each lot would vary by no more than two tenths of a grain.

This level of selectivity resulted in roughly half of my brass being discarded. i.e. out of 300 cases, about 150 fell into one of those 3 lots.


generally, I've found my lapua brass to be a little more consistent (unfortunately, they don't make brass in 6xc) and winchester brass to be considerably less consistent.

 

[taliv]

let me add that i was just weighing the actual brass. I think a lot of precision reloaders measure actual case capacity by filling it with water and weighing the water instead of the case.

 

[cracked butt]

Heavier cases will have extra brass somewhere which equals slightly less case capacity. Slightly less case capacity with the same powder charge equals higher pressure.


It seems like it would only make much difference if you are loading very hot loads and are looking for the very best accuracy.

 

[USSR]

Does anyone have knowledge about loading cartridges with different case weights? I find 4 to 6 grains weight difference in the same brand cases & I'm wondering how much this affects the performance...... should powder weight be adjusted to compensate? I have not found any case weight data in any loading manuals.

SgtMajor,

For hunting loads or loads designed to be used in a spray-and-pray type of application, the weight variance is of no consequence. However, if you are developing loads for accuracy, and in particular, long range accuracy, then I would suggest sorting by weight. What I typically do with my LC M118 Match brass is find the median weight and sort into 3 batches with a 1 grain variance within each batch. The first batch is all cases that fall within 1/2 grain on either side of the median weight. The second batch is all cases that fall within 1 grain of the low cut off point of the 1st batch. And the third batch is all cases that fall within 1 grain of the high cut off point of the 1st batch. The remaining cases that fall outside of the weights of the 3 batches are used for load testing and fouling shots. There is no need to adjust the powder weight for the 3 batches, just shoot cartridges from one batch each time and don't mix them. Hope that helps.

Don