Russian WWI-era Mosin-Nagant Infantry Rifle, Model 1891/1910. This rifle has all the arsenal "upgrades" up through 1910 and was most likely otherwise refurbished/repaired each time. Originally manufactured circa 1899 at the Tula Arsenal and so stamped on the receiver.
This example was imported by Century Arms International and so marked on the barrel near muzzle. Fixed box magazine, 5 rounds, 7.62 x 54R caliber. Overall length ~51-1/2".