In the latest issue of the Colt Collector's Magazine, "The Rampant Colt" there is an article entitled: Colt Two-Inch Revolvers in U.S. Military Service by Kevin Williams. In that excellent article Williams mentions that, "A special low pressure cartridge was developed (Cartridge, Ball, Caliber .38 Special M41)...." for use in the aluminum frame and cylinder Colt and S&W Aircrewman revolvers. This took place in the early 1950's, so that would seem to be the origin of the M41 load.