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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.
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.
