Hi late to the party but I agreee with the-man and mi buddy Monty. it is of modern comtruction as the rifleing if for a fairly hard jacket. If it had been in the civil war, they used lead for the projectiles and hence had much wider lands ro keep from slipping too much. My guess would be a .45 semi auto pistol projectile, or a submachine gun utilizing the same ammunition using the lands/groves as a measurment.
Tropical Tramp