I’m aware of what caliber a 9mm measures; my point was that the original phrasing could’ve been a cute way of drawing a line between the inadequate .380 and the 9/40/45, since 9>4.
And despite what 10 millimeters converts to, if a 10mm cartridge fired a .395 caliber bullet then there are a lot of people shooting .395 S&W right now, since the .40 is just a chopped down 10mm case that fires the same bullet.
(Albeit much, much faster...energy on par with the .357 Magnum, or 50% more powerful. I still don’t understand why the FBI declared it too powerful for everyday use...everyday use is holstered. On the rare case when you have to fire, why wouldn’t you want a substantially more powerful but still very controllable round?)
I had forgotten that .40 was effectively a 10mm short. You’re right.
Things I’ve read about the .40 are that JHP loads seem to be designed to meet the FBI’s own “12 inches of ballistic gelatin” guideline more closely than any other caliber. I don’t see what they don’t like, unless they feel their own guidelines are overkill.