If it has "V/P/(eaglehead)" on the barrel breech, "US" on the tang of the buttplate and and the inspector's initials on the left side of the stock, opposite the lock, it's a Model 1861 U.S. Percussion Rifle-Musket. The lock, trigger guard and rear sight look right from this one photo. The other marks mentioned will make additional confirmation more certain. This was the improvement over the M.1855 in that it eliminated the troublesome Maynard priming system, hence the humped up hammer. The total production was around 1,000,000 during the Civil War and surviving original model from Springfields with the original 1861 date are valued 25% above all the contract guns made by known 22 contract makers. Congratulations! Hope the bore and stock or in equal shape.