This is an original Colt Iron Bullet Mold. Sprue cutter is marked COLT'S PATENT and left side of the mold is stamped "36B" which stand for Belt Model. According to Robin Rapley's book on Colt Accoutrements, this mold is correct for 3rd and 4th Model 1851 Navy Models and the 1861 Navy.
This one is in Very Good Condition with a fairly smooth brown patina overall with strong traces of original blue in protected areas. Colt's Patent is clear on the sprue cutter. Conical and spherical ball cavities are in Excellent shape with most of the original blue remaining on the internal surfaces. Should pair nicely with Colt 1851, 1861 Navy Revolver, or in a factory wood case.