The Black Transitional Two Position Cam scope was produced in 1976 by Leatherwood Brothers in a consortium with Military Armament Corporation for use on the M-21 rifle. The two position cam allows the scope to be used with both standard M-118 ammo and subsonic M-118 loads developed by Leatherwood/MAC for use with the Sionics/MAC M14SS-1 Suppressor. The double knob/notch system allowed the shooter to switch between calibrations in the field very rapidly with no special tools required.
Of the 422 Black Transitional ART 2 scopes produced for Special Operations Groups only 122 of those used the two position cam system. Of those 122 only two units are known to have survived.