>>64093907
The "10mm is just expensive 40" fuddlore comes from Federal loading some of their ammo to the old FBI spec that eventually became 40 S&W. It's a pointless thing to bring up anyway since nearly everyone nowadays shoots weak bulk ammo for training and carries hotter ammo for defensive purposes. The only distinction is that there's no such thing as 10mm +P, because 10mm is a modern cartridge that didn't require the +P designation like 9mm and 45 ACP, which both have lower pressure SAAMI specs for their case capacity due to being over 100 years old.