Both the M1C AND the M1D were sniper versions, of the trusty old warhorse, M1 Garand.
The M1C was an interim rifle while the armorers worked on an improved version which would be known as the M1D.
The "D" had a 4 power scope, a flash suppressor and a leather tie on cheek piece on the butt stock.
Original "D"s are fetching a pretty penny now. The DCM (Department of Civilian Marksmanship) had a few "C"s and "D"s that they were selling. But, that was a couple of years ago.
I saw an M1 at a gun show in Tulsa a few years back that had a $10,000.00 price tag on it. The rifle also had documented proof that it had been checked out of the arsenal on the U.S.S. Arizona, for guard duty on the night of December 6, 1941!!!!!!!
Would have been something to own. But, alas, I am a shooter and I couldn't have owned it for fear that I would take it out, shoot it and ruin it's value. And besides......I didn't have an extra 10 grand laying around!!