9mm case data
Every reloading manual I have says that cases should be separated by head stamp before reloading. I assume the reason for that is because of significant variations in case size and volume from one maker to another. So I decided to find out how much variation there is in the calibers I will reload - 9mm and .40 S&W.
I separated just over 500 9mm cases by head stamp. Next I took 20 random cases from six of the most common brands (120 cases total). I weighed, measured total length, and wall thickness of each one by brand. The results are posted below.
There is a lot of variation within brands and from one brand to another. The biggest variation is in the weight of the case. The cheap Federal cases vary as much as 6.5 grains from highest to lowest weight. Winchester is next with over 5 grains difference from high to low. The least variation is the Blazer with 1.6 grains from high to low.
If you combine all the results the weight can vary by 8.5 grains. That seems like a lot.
What I am trying to figure out is what impact the case weight variance has on the loaded cartridge. There does not seem to be any correlation between wall thickness and/or overall length and weight. So if that is true (and I'm not sure it is) a heavier case might indicate a lesser case volume because the extra weight would take up more volume.
The next question is what can you do about the weight variance and is it important? The only answer I can come up with is - nothing. And it must not be very important because no one seems concerned - at least for straight sided handgun cases.