Same thing on the 1911A1 pistols. Colt oven (heat) blued their pistols up until the July 1941 time frame when they changed over to phosphate. Ithaca, Remington Rand, and US&S Du-Lite blued theirs over a sandblasted finish. Ordnance changed the specifications on the finish, requiring a Type II (phosphate) finish in late 1942. The manufacturers were given time to install the necessary equipment to change to the phosphate finish, and Ithaca and Remington Rand changed to phosphate in the July/August 1943 time frame. US&S had their 1911A1 contract cancelled, and ceased production before changing over to phosphate finish.