Which doesn't begin to explain the .38-40 cartridge from the 1880's, since the bullet has a .40 caliber / 10mm diameter.
How the heck did that happen?
They wanted a bullet with similar flight characteristics of the 44-40 but the 200 gr 44 caliber bullet with 40 gr of black powder was considered too stout for some shooters. drop 20 grains and reduce bullet diameter to .401 instead of the .427 of the 44-40 and marketing steps in with a smaller number of 38. I have never ever found a good solid reason for calling a 40 caliber bullet a .38 because going by convention back then they should have named it the .416 or the 41 or the 42 because of the .416 neck diameter of the case. Never ever try to follow the logic of marketing, it will drive you nuts.
Good intentions will always be pleaded for any assumption of power. The Constitution was made to guard the people against the dangers of good intentions. There are men in all ages who mean to govern will, but they mean to govern. They promise to be good masters, but they mean to be masters.