That is an interesting "replica" cartridge. I am glad the maker marked the case body with an "R". I have no knowledge of a belted U.S. .30 caliber cartridge.

When I first saw the "U.S.G." head-stamp, I thought it was made from an early .30-06 Commercial Case. (Since, ".30 Government" is sometimes marked on .30-06 commercial rifles).

I knew the .30-40 was also called .30 Army or .30 U.S.A, but, I was unsure of the .30 U.S.G. name being applied to the Krag cartridge. It didn't take much searching to find a picture of a regular/old .30-40 cartridge with the "U.S.G." head-stamp.

I wonder if a 'belted-rimless' .30-40 cartridge (if it should exist) could have been an experiment in a .30" Gatling Gun or Colt Model 1895 "Potato-Digger" Machinegun?