>> .22 bullet is 0.22" across (duh)

Um... No. An american 22 can be very slightly smaller. American-invented calibers are measured to the depth of the grooves in a rifled barrel. The rest of the world measures to the flat parts between the grooves. So no, it is not obvious how wide a bullet is.

And beware the plural. If someone (usually a salty navy person) says that a gun is "50 calibers" he means something completely different than a "50 caliber".

https://en.wikipedia.org/wiki/Caliber

Wow, I had no idea. The ones we had at the range were 0.22LR and the boxes are marked 5.7 mm which is also not precisely 0.22".

Yeah, given the nominal precision it's surprising how far off some of the numbers are. A .38 is the same diameter as a .357.