"Rear Sight Assembly - The standard issue rear sight aperture has a diameter of 0.069 " + 0.005 ". The USGI M14 also had two National Match rear sight aperture sizes, 0.0520 " and 0.0595 ". Either National Match rear sight aperture can be fitted with an adjustable hood (National Match rear sight apertures without the hood were made only for the M1 Garand rifle). Use of the hood on the rear sight allows for one-half minute of angle adjustments in elevation. The elevation knob always moves point of impact one minute of angle per click, while rotating the sight hood will add or subtract a half-minute of angle of elevation. A notch in the rear of the hood designates the direction of the extra adjustment—rotating the notch from the six o’clock position to the twelve o’clock position will add elevation, while rotating the notch from the top position to be on the bottom will subtract elevation. The hooded eyepiece was developed by no later than May 1961 at Springfield Armory by Nicholas J. Angelica.
Rear Sight Base - The M14 standard (rack grade) rear sight base was borrowed from the same 1937 vintage part for the M1 Garand rifle. Additionally, three other rear sight bases could fit the M14 rifle. These rear sight bases were marked NM, NM/2 and NM/2A. The NM rear sight base was designed about 1958. It accepted a non-hooded rear sight aperture but would not allow a hooded aperture to fully lower into the base. The 1961 design NM/2 rear sight base was a NM rear sight base machined after manufacture to allow a hooded aperture to fully seat in the base. Subsequent to the NM/2 modification, the 1963 design NM/2A rear sight base was a newly manufactured part that allowed the rear sight base to be fully lowered into the base.
Elevation and Windage Knobs - The M14 type elevation knob will have the letter M inscribed on it between the numbers 10 and 11. This denotes calibration in meters. If the elevation knob does not have a letter M, the knob is calibrated in yards and was made for the M1 Garand rifle. As a rule, M1 Garand rifle elevation knobs were not allowed on M14 rifles in the U. S. military. However, for a period of four months or less in 1969, M1 Garand rifle elevation knobs were authorized for replacement of M14 elevation knobs on M14 rifles at Fort Bragg. During this time, there was a shortage of M14 elevation knobs in the Army supply system. The elevation knobs on the M14 rifles at the Basic Training shooting ranges had worn out from use by recruits. In order to keep the M14 rifles in service for training and qualification, Rock Island Arsenal authorized the short term substitution of M1 Garand elevation knobs for the M14 rifles.
The windage knob on an M14 type rifle will either be the standard one minute per click adjustment, or the National Match model of one-half minute of angle per click adjustment. The National Match windage knob must be matched to a National Match rear sight base because they both have finer threads than the standard USGI parts. The finer threads of the National Match rear sight parts allow the smaller angle adjustments."
