Jesse:
I don't know whether or not you're crazy. You'll have to ask Mrs. Jesse for a definitive answer on that item. Better not to ask. I would never ask my own lady that question, for fear.
Now, back to work:
As it happens, 10mm = 0.3937 inches [which clearly ain't .40 cal. Just like you said up above.]
But then, .38 cal and .357 cal both fit into the same cylinder of my Model 19 S&W. And they both go through the same barrel, just alike.
For fun in slow times, you could get out your micrometer and measure the diameter of a .38 caliber bullet. It isn't .38 caliber and it isn't .357 caliber. It's a whole something else different.
So........ammo-wise, you're not crazy.
It's the ammo designers, manufacturers, and----most of all----the AMMO Namers!!!!!
They are as crazy as a gaggle of weasels.
SemperFiGuy