The information below is from Instagram.
Images showing officers of the then Single Force of Jalisco (image 1 to 3) and Special Forces of the Secretary of the Navy (image 4 and 5) carrying Colt CM901/LE901 caliber 7.62×51 NATO rifles.
The modular carbine grew out of Colt’s need to offer an AR-10 platform that could fill a role in its catalog as a select combat/marksman rifle and would begin development after Colt failed to purchase ArmaLite, so it was would be forced to design a rifle instead of selling the ArmaLite as planned, this rifle would be based on the semi-monolithic prototypes that Colt designed for the S.C.A.R. program, the 7.62 NATO caliber platform lower receiver has the ability to accept 5.56 caliber AR-15/M4 upper receivers/drawers with the insertion of an adapter block, which secures the upper receiver to the lower receiver and adapts it to feed from STANAG 5.56 magazines.
The Colt CM/LE901 has not seen much adoption, as far as I know no military units have adopted it and it has only been purchased by law enforcement agencies in the United States as a select marksman rifle, so it is very interesting to see that at least used or tested in our country.