If you measure the bore of a ".38 Special" revolver, you'll find that it measures only 0.357". So it's not even a 36 caliber! Hal
@Hal Pollner But measure the cartridge case OD: .38". This difference applies to many small-arms calibers, but changes to bullet diameter call-out in rifle cartridges, generally. SEE: https://en.wikipedia.org/wiki/Caliber