The 318 WR aka 318 Rimless Nitro Express aka 318 Westley Richards accelerated Express is not a 318 caliber at all but a .330 caliber. (8.38mm)

There was one other cartridge of similar bore diameter and that is the .333 jeffery.

In very remote pre modern history there are a few BP cartridges from Germany that came close in bullet diameter in the form of 8.35 mm caliber.