M1D sniper rifle with M84 scope is shown above an M1C sniper rifle with M81/M82 scope.
FM 23-5 - (MAY 1965) U.S. Army Field Manual for the U.S. Rifle, Cal. .30, M1
TM 9-1275 - (JUNE 1947) - Maintenance U.S. Rifles,
Cal. .30, M1, M1C, M1D
To Zero the M1
The original rear sight of the M1 would not hold adjustments very well, so a locking bar was added in late 1942 which could be tightened after sights were set. This is
shown in the M1C. An improved sight, the T105, was standardized by the end
of WWII, and is shown on the M1D, above.
Each click of either elevation or windage changes the strike of the bullet approximately one inch on the target for every 100 yards of range, over its effective range.
One click will move the bullet strike:
1 inch at 100 yards
2 inches at 200 yards
6 inches at 300 yards
12 inches at 600 yards
Windage can be adjusted 16 clicks to the right or to the left of center index, and elevation can be adjusted from 0 to 72 clicks.
Remember, to be able to get consistent hits, the rear sight must be zeroed for the various ranges, and the sight setting recorded, and should be kept in the accessory compartment of the stock for reference. To move the mean point of impact up, raise the rear sight. To move the mean point of impact to the right, move the sight to the right, and so on.
The battle sight setting is the 300-yard zero, less two clicks.