I haven't shot any for a bunch of years, but got started on them in the mid 1970's.

Actually, the 1873 .45 Colt Revolver had a(bout) a .454" groove diameter and shot .454" bullets.

The model 1860 Army used .451" to .454" balls in the slightly undersized cylinders, but also had "about" .454" groove diameter.
Because the bore diameter is "about" .44(something), they were called .44's, same verbiage used in muzzleloaders, most English & many European CF rifles & handguns where the bore diameter is called the calibre, not the groove to groove diameter. Named by groove diameter appears to be a "later" American & Euro. designation. Of course, they also named some calibres verbiage that had nothing to do with any actual dimensions of the gun (.44 Spl., .44 mag., .444 Marlin)