The Army began around 1930 to "rationalize" ordnance model numbers, beginning with M1 for everything, so there wan an M1 rifle, M1 carbine, M1 SMG, M1 canteen, M1 helmet, etc. Naturally,, the full nomenclature was rarely used.
Just FWIW, in service the M1 carbine was never called the "M1", that term being reserved for the M1 rifle. The M1 Carbine was just called the "carbine", as "That's my carbine over there." If for some reason there was a need to distinguish an M1 Carbine from an M2 Carbine (the M3 Carbine was unknown) the term would be "M2 Carbine" or "M1 Carbine".
The term "M1" alone in reference to an individual weapon always meant the M1 Rifle, and it was rarely called by any other term. In the very early (pre-WWII) days, the rifle might be referred to as "the Garand" but by the start of WWII, the Johnson and other rivals were gone and the rifle was called either the "M1" or simply "rifle" (as in "that's my rifle").
The other "M1" in common use was the M1 Thompson SMG, almost always called the "Tommy gun" whether the M1928A1, M1 or M1A1. The later M3 and M3A1 SMGs were universally called "grease guns" from the resemblance to the automobile maintenance tool.
Jim