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I recently separated a batch of range pick-up 9mm brass by head stamp. I believe there were 9 different brands of cases. The six most common were, WCC (nato), FC (Mexico), FC (USA), Blazer, Win, and PMC. I weighed and measured a sample of 20 of each.

My purpose in doing this was to find how much variation to expect from case to case. The short answer is a lot - much more than I expected. The most surprising finding was that almost 50% of the cases I measured did not meet SAAMI standards for case length.

The SAAMI standard for 9mm cases specify a maximum length of 0.754" and a minimum length of 0.744". Of the six brands I measured PMC was the best in terms of case length with only 1 of 20 that was out of spec. Blazer was the worst with 16 of 20 out of spec. The others all had from 10 to 14 of 20 out of spec.

Not a single case was over long they were all short. The shortest was 0.737. Only two of the six had an average case length that was in spec. Those were FC-Mexico, and PMC.

Now my question is does the short case length have any meaningful effect on the cartridge? If the rounds are loaded to a constant over all length some will have a little less of the bullet inside the case - just a few thousands less. Does that have any impact on pressure inside the case or does anyone know?

I've attached the SAAMI drawing and the spreadsheets with the raw data.
 

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