Cheesehead
I would just keep them and definitely would not shoot them.
1.They were made before or around the time of the Union Metallic Cartridge/ Remington Arms Company merger which occured in 1911. Some time after the merger headstamps are Rem-UMC.
2.The primers will be corrosive. It wasn't until 1926, Remington introduced Kleanbore priming in ammunition.
3. It is possible to have a blackpowder round. My 1901, 1903, 1908, and 1910 UMC catalogs have both in them. Remington listed blackpowder revolver cartridges until 1938 catalog.
4. My 1913-14 catalog shows UMC headstamp in cartridge pictures.
rem2035