IIRC - Frankford Arsenal developed a rimmed, smokeless, .30 caliber cartridge that was used in some of the arms entered in the 1892 and 1893 trials. This evolved into the .30 U.S. Army cartridge.

The possible trial Mauser rifle may be chambered for the .30 F.A. rimmed cartridge. The '.30-40 KRAG' marking is likely a much later hand-stamped addition.

I believe some late trap-door rifles were used to test .30 caliber rimless experimental cartridges that became the .30-03 cartridge.