Because your .50-70 brass casing does not have a steel base-disc, and it does have a small-ish central primer-cap, it's not one of the "early US Military .50-70 cartridges" shown here:
https://www.oldammo.com/november06.htm
The version of external primer-cap in yours was patented in 1872, so they can't be from any earlier than that. Because your .50-70 casings do not have a headstamp, AND the bullet seems to have a small flat nose-tip, I'm guessing it is the version shown in the 2nd photo here, 1st (and cutaway 2nd) on the left of the row.
> https://www.oldammo.com/december06.htm
Several of the casings in the photos have a brass base-rim which is beveled at the bottom edge of the rim. I can't tell from your single photo whether or not yours have the beveled-rim bottom. So, you'll have to closely examine yours in real-life and figure out which (if any) of the ones in the photos matches exactly with yours.