When the finish of the 1911A1 pistol was changed from blue to phosphate, the barrel and magazine was still blued through the end of production. The tops of the magazines were tempered to keep the lips from bending out of shape, and this hardened area sometimes shows up a slightly darker color when the magazines went through rebuild and had a phosphate finish applied. The hardened area in no way affects the phosphate finish.
Does anyone know if any Carbine bolts were rust blued? The rust blue process was labor intensive and I just can't see it being used in WWII. Springfield last used rust bluing in 1918.