The 30/40 is a killing machine. Somewhere in history (before I was born) my mother's M 95 was lost. Rumor has it that my mother was a "hell of a shot."
I have never used one, but being from Montana I know a lot of oldsters who tried other "more modern" rounds who went back to the "30/40 Krag" and swore by it.
The other old rounds that I remember were used by many of the older generation, back in the 1960's when I was a kid and loved to read about the "latest and greatest" developments and ask questions, were the 33 Winchester and the 348 Winchester.