You may want to go to a gunsmith to find out the caliber. For these guns there are two common calibers when sporterized. Number 1 is 6.5x52 Carcano (the original caliber it was in), number 2 is 6.5x54 (some were converted to this caliber).
As a side note this rifle isn't a Mosin look alike, and the only thing the designs have in common is a split bridge receiver, if anything a Carcano is more a 1888 Commission rifle modernized (by 1891 standards). Both the Mosin (model 1891) and the Carcano (model 1891) were developed in the same year. After WWI and WWII several companies (cooey being a big one) sporterized the Carcano to make them hunting rifles. Some (most?) have double triggers, and a fair bit were converted to 6.5x54 (6.5 MS).