Ruger hand stamped the 'D', which seldom aligned well with the rest of the serial number. Prior to the Gun Control Act of 1968, Ruger didn't manage their serial numbers very well so sometimes two guns ended up with the same serial number. The 'D' prefix in the serial number stands for 'duplicate S/N'. They had real walnut stocks, metal trigger group, metal barrel band, and a metal butt plate, all being very desirable and adding about $100 to the normal value. The earlier 10/22s like yours were quite a gem.
