DonP, we don't have to agree.
I just started reloading 9mm.
I bought a bunch of Remington ammo for the brass.
I also bought 1,000 rounds range brass.
Using the Misc Brass and the Remington brass I get a difference of one half the Extreme Spread. Sometimes its only one shot in 10 to throw it off.
I do not have that problem using all the same headstamp brass.
This is the same load, powder charge, bullet, primer and dillion press.
Max SD with sorted brass is between 6 and 15 depending on powder and bullet.
With mixed brass its 22 to 30.
I also find the ES or SD with mixed brass is greater between a 3" barrel and 5" barrel.
With CFE pistol, matched brass and Nosler 124 HP, I get SD of 6 in the 5" and 8 in the 3"
Take it for what its worth. I load for consistency.
David