MIL-S-45921A, MILITARY SPECIFICATION: STOCK, GUN, SHOULDER: ASSEMBLY W/O BUTT PLATE, FIBERGLASS REINFORCED, PLASTIC (PREMIX) (FOR RIFLE, 7.62MM: M14) (22 JUN 1993)., This specification covers one type of fiberglass reinforced plastic (premix) stock assembly for the M14 rifle. The stock assembly is furnished without the butt plate but with the slotted machine screw, square plain nut, and nut retainer required for assembly of the butt plate (See 6.1).