Very nice collection of M1C and M1D rifles. Congrats on putting those together. My guess is you'll like the M1C with Kollmorgen best for shooting, given the scope has 4X magnification and has coated lens that allow better light transmission (its also much larger in diameter, 26mm vs 7/8").
Since we are on the subject of M1 Garand sniper rifles, there is actually one more odd-ball variant of the M1D sniper, which I will call the "mid-1960s version" or "the 1-inch scope mount version". The acquisition of the scopes and who actually used these late M1Ds made in the mid-1960s is a bit of a mystery, but basically International Armament Corporation and American Firearm and Ammunition Corporation (INTERARMCO) purchased 2,531 of the 1" scope brackets that were modified version of the original 7/8" M1D scope brackets, along with 2,445 Weaver K4 scopes.
They were delivered between Oct 1965 and July 1966. Supposedly for National Guard units, but the history is murky, and some may have made it over to Vietnam in the early years of that conflict, although the M1D with M84 scope is far more commonly referenced. (The owner of INTERARMCO, Sam Cummings, had warehouses in Virginia and the UK, and supposedly might have helped move surplus firearms around the world for potentially clandestine activities and/or anti-communist campaigns on behalf of the CIA, but who knows, that is some rank speculation that I read.) It is important to note that the M1D was still the official sniper rifle of the US Army until 1972, when the XM-21 became the M-21 and replaced the old 30-06 M1Ds as the Army's official sniper rifle, so the order for the scope & mounts in 1965-66 was for an active weapon system.
The specific US military customers (or National Guard, or maybe even the CIA...) who received these 2500 optic systems in the mid-1960s is not clear, but I will note that some articles written 30 years ago showed that a small number of these rifles with 1" mount and 4x Weaver scopes were still in USMC inventory (1989) and US Special Forces (1990) also had some in their inventory for training and familiarization purposes. (Scott Duff wrote about these in 1990, before the documentation was uncovered in the archives). This M1D configuration doesn't appear in any Technical Manuals, but the archives at Springfield Armory helped reveal the origins, dates, and volumes of the scopes and mounts delivered to INTERARMCO.
Anyhow, the US Army transferred these old Weaver scopes and 1" mounts to the DCM (now CMP) in the early 1990s, and they subsequently sold these somewhat rare 1" M1D mounts and Weaver scopes to the public in the mid-1990s for I think $175 for the combo. That is where mine came from via an old collector who was selling off his collection years ago. I do shoot this M1D from time to time and I like this set-up, even if it is a bit odd. Just a random factoid to illustrate that there were basically two M1C optic system configurations over time, and also two M1D optic system configurations overtime. I consider this configuration as the 'final' variant of the M1D sniper rifle.
