The M.O.A.B = Minute Of Angle Base, scope-base system was first designed in the late 90’s, to compensate for the lack of vertical adjustment in modern rifle scopes. Further, it was designed to eliminate the problems associated with distortion caused by “bending” light through as many as (10) lenses within modern scopes.
Today, every major scope manufacturer, offers a wide selection of, ”bullet drop compensating” reticles, and “custom” turrets. The problem with these expensive features is that they are only correct for ONE cartridge, with ONE bullet weight, at ONE velocity.
The M1A/M14 is a weapon specific mount with up to 300 MOA adjustment. This model mounts in the rear sight ears and also to the front left side of the receiver with the standard 12-32 mounting bolt into the predrilled and tapped hole of your receiver.