This Ruger manufactured 5 1/2" long bull barrel with front sight is for the Mark I semi-auto pistol equipped with an adjustable rear sight and is in very good condition with a mixture of original blue finish and a brown patina and possibly a few specks of surface rust. The bore is bright and rates near excellent.  (file photo)

Note: Ruger Mark I semi-auto target pistols with the following serial numbers have been observed with this barrel: 10-90939