when you say precisely do you mean inside diameter and length of shell casing?Can you measure them precisely? If we can determine what caliber they are that will help quite a bit in determining the age. I can tell you they weren't fired in a Henry rifle since there is only one firing pin impression, but that's about it.
The US Cartridge Company was founded in 1869 in Lowell Mass, and was eventually bought out be Winchester in 1926.
the shell diameter is 1/2 inch and casing length is 7/8 inch. thanks.
thank you very much for the information.Ok, I'm going to say you most likely have .56-56 Spencer shells there. They were made commercially up into the 1920's by a few makers, I really can't narrow it down any more than between 1869 and 1926 at the moment. I can't find any info on when US Cartridge Co made them.