Mystery Cartridge, hints wanted.

[RCS]

The Russians used the early round nose FMJ 210 gr bullet until replaced in 1908 by the 148 gr spitzer bullet (which took years to replace)

The US Cartridge headstamp on your cartridge has the early Russian round nose bullet

I have a 45-70 case with the US Cartridge headstamp too

Photo shows early Russian pre 1908 cartridges in a clip