Why Were Carbines Factory Parkerized When ALL USGI Thompsons' Were Factory Blued?

[BrianQ]

Qhmc used round center punch marks on some of the flip sights they used and Inland used a chisel like stake mark on some if the adjustable sights they used.

Others used which ever was the appropriate tool to use for the task, sometimes using both.

[Tobor]

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.

And yet Savage & AO continued the use of the Du-Lite Type III Black oxide finish on the TSMG until production ceased February, 1944. This departure from what other WWII government contract firearm manufacturers were doing regarding Parkerizing appears to be an aberration at the time.

[emmagee1917]

...at this point in time , carbines , garands ,Bars, M1911s , M1919A4s , etc. were still primary , standard classed weapons. M1928 thompsons were limited standard with the M3 and M3A1 greaseguns as the then current standard. It was just unwise , with the war and all , to justify the time and expense to install the parking equipment in plants for a weapon system that would be shortly discontinued when M3 production met demand ( and the M3 was parked).
Chris

[Johnny Peppers]

Late in 1944 Colt was allowed to change to Parko-Lubrite. The first picture is of a June 1945 Colt 1911A1 finished in Parko-Lubrite. The receiver and slide were not sandblasted before the finish was applied, leaving a very smooth finish, but one that shows the machine marks.
The second picture is of an April 1945 Colt with a Parko-Lubrite finish, but the receiver was sandblasted before finish and the slide was not.
On the sandblasted receivers care was taken not to sandblast the top of the receivers or the feed ramp which left them very smooth, and Ordnance did not require Colt to polish the finish off the feed ramp.

[Tobor]

...at this point in time , carbines , garands ,Bars, M1911s , M1919A4s , etc. were still primary , standard classed weapons. M1928 thompsons were limited standard with the M3 and M3A1 greaseguns as the then current standard. It was just unwise , with the war and all , to justify the time and expense to install the parking equipment in plants for a weapon system that would be shortly discontinued when M3 production met demand ( and the M3 was parked).
Chris

It is true that the M1928A1 was reclassified as "Limited Standard" in April, 1942, but at the same time, the "new" M1 TSMG was adopted as Submachine Gun, Caliber .45 M1. Then considered as "primary standard classed weapons." By January, 1943, the M1A1 (fixed firing pin bolts)TSMG was being manufactured. These had the same Du-Lite Type III Black oxide finish. By January 1943, AOC was told that the M3 Greaser would replace the TSMG. Had there not been manufacturing problems with the Greaser, the TSMG would have ceased production in April, 1943.