.44 Mag shotshells from .30-40 Krag and/or .303 British cases.
.44 Mag from .30-40 Krag and/or .303 British. (Sounds the same as above, but it's a very different process and end result.)
.410 loads in .444 Marlin.
.243 Winchester from .30-06. It sounds simple, but it's a helluva lot of work.
Anything else just involves pushing shoulders around, changing case length, and/or changing neck diameter.
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."