You are correct, Mr. Bart Noir. The Browning Hi-Power was made in that caliber as well as the Sig P-210 in Switzerland. The .30 Luger was the Swiss service cartridge. According to Wikipedia, other handguns were also chambered for it, more so than I realized, but I recall seeing advertisements for the Ruger P-something that came with two barrels, one in .30 Luger, the other 9mm.
I was also aware the Japanese used more than one cartridge in 7.7mm, the different designations of which I did not look up. That's why I said "a certain Japanese." I knew about the Lewis gun copy, didn't know about the Vickers. The semi-rimmed version may have been used in their copy of the Hotchkiss but I don't have any reference material at hand.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.