The M1C was an M1 Garand with a telescopic sight, using a mounting system developed by the Griffin & Howe company of New York. It utilized a rail pinned and screwed to the left side of the receiver, coupled with a quick-release scope on top. The rails had to be installed prior to heat treating the receivers, which had the unfortunately consequence of preventing rifles form being chosen for sniper conversion based on their mechanical accuracy. Instead, accuracy would be tested only after rifles were complete, leading to a 60% rejection rate.
The scope was offset to the left of the receiver so as not to interfere with the Garand’s clip loading, and issued with a leather cheek pad to give the shooter’s cheek weld a matching offset to the left. The scope used with the M1C was the M73B1, later replaced with the M81 and M82 scopes - all military versions of the 2.5x Lyman Alaskan hunting scope (which was a very good piece of equipment despite its low magnification)
The M1C was adopted in 1944, but production and quality control delays would prevent it from seeing any action in WWII. It was in use during the Korean War, however, before being replaced by the M1D.
Japanese Type 97 Sniper: https://www.full30.com/video/c9f4b7e4f9bdc78f5d8e8cf9fb5cec56
US WWI Sniper Rifles: https://www.full30.com/video/65a7a1b20b01b0776658c42108d794b9
ZF41 Scout Scope: https://www.full30.com/video/5968e95ab5647908f5a6d7ec708ecfa8
2 Gun Action Match - G43 w/ ZF4: https://www.full30.com/video/eb6179349a4e5212f0faede7af6ba7be
M1D Sniper Garand: https://www.full30.com/video/76fe1adfc8f1273420065c1a14c43fcf
MC-1952 Sniper Garand: https://www.full30.com/video/b6111dfde163c1e79d9552fe1120b16d
M1903A4 Sniper Rifles: https://www.full30.com/video/f7b62b7c1e1c7d8b57bd64e6f78b59c5
M70 Vietnam Sniper: https://www.full30.com/video/572ff4f9d6a8d4848a0f74b4a10362aa