If this rifle is not the 1871/84 it may have a .457" groove dia.
My rifle was a 1871/76 Carbine and it had the typical .457" groove dia.
The only trouble with that, is that the chamber's neck will only allow a .446" bullet to be seated in the case.
There was some thought at the time that deeper grooves would help prevent fouling problems.
A paper patched bullet will likely be the best shooting projectile if this rifle does have the .457" groove diameter. The rifling depth in these was .011".