This is a private purchase Model 1912 style holster. The Model 1912 holster was never very popular with the troops, but I guess the Colonel that this holster belonged to favored the look of the Model 1912.
Pictured also is the 1924 Transition that came in the holster.
https://www.milsurps.com/images/impo.../2lk4t2s-1.jpg
https://www.milsurps.com/images/impo.../11aldl2-1.jpg