It is a New York State rolling block rifle, used by the New York National guard from approximately 1872 to 1897. Approximately 15,000 were ordered in 50-70, very, very few were made in 45-70. You will need to do a chamber cast to determine which one it is.
You might remove the steel butt plate and see if
anything is stamped in the wood. Buffalo ordered
rifles of the same pattern used by N.Y. state but
in 45-70. These were stamped with "BCG" for
Buffalo City Guard.