I need a partial serial number. The 31 was made in three different series, and the barrel lock assembly was changed each time. The first series,made from 1931 to 1936 had what is described as a "spring-up" (?) barrel latch assembly. The other two series had a "screw-up" assembly. The barrel lock nut (if there is one) should partially unscrewed by turning it to the left. Then partially open the action and turn the barrel 90 degrees to the left and pull it forward.