Caliber is bore diameter. Cartridge is 9mm Luger, 9 mm Kurtz, etc.
Does it matter if everyone understands the message and intent?
I want to pare down my carry pistols to a single caliber, between 9mm, .40S&W, and .45acp. Which do you think is the best single caliber and why?
I'm leaning toward 9mm because of variety, price, and reliability.