Rare .36 Iron mould with sprue cutter, for London manufactured Colt Model 1851 Navy percussion revolver. Straight leg mould, stamped “COLT’S PATENT” with an apostrophe, on the top face of the sprue-cutter, close to the hinge. The two cavities are for a round ball nearest the hinge pin and a conical with a heel grease groove below it. The groove helps facilitate loading into the cylinder chamber. The locating pin is on the left leg, on English manufactured moulds and the depth of the mould is 19.90mm against 20.05mm on American manufactured navy moulds. In many instances, it is difficult to insert an American made Navy mould into a London made case circa 1853 to 1857, without forcing it in. The finish is blue.