▁variants , ▁never ▁saw ▁active ▁duty . ▁The ▁sni per ▁versions ▁were ▁modified ▁to ▁accept ▁scope ▁mount s , ▁and ▁two ▁versions ▁( the ▁M 1 C , ▁formerly ▁M 1 E 7 , ▁and ▁the ▁M 1 D , ▁formerly ▁M 1 E 8 ) ▁were ▁produced , ▁although ▁not ▁in ▁significant ▁quantities ▁during ▁World ▁War ▁II . ▁The ▁only ▁difference ▁between ▁the ▁two ▁versions ▁is ▁the ▁mount ing ▁system ▁for ▁the ▁teles cop ic ▁sight . ▁In ▁June ▁ 1 9 4 4 , ▁the ▁M 1 C ▁was ▁adopted ▁as ▁a ▁standard ▁sni per ▁rif le ▁by ▁the ▁U . S . ▁Army ▁to ▁supp lement ▁the ▁v ener able ▁M 1 9 0 3 A 4 , ▁but ▁few ▁saw ▁combat ; ▁w art ime ▁production ▁was ▁only ▁ 7 , 9 7 1 ▁M 1 C s . ▁ ▁The ▁procedure ▁required ▁to ▁install ▁the ▁M 1 C - type ▁mount s ▁through ▁dr illing / t apping ▁the ▁hard ened ▁receiver ▁reduced ▁accuracy ▁by ▁war ping ▁the ▁receiver . ▁Im pro ved ▁methods ▁to ▁avoid ▁reduction ▁of ▁accuracy ▁were ▁in efficient ▁in ▁terms ▁of ▁tool ing ▁and ▁time . ▁This ▁resulted ▁in ▁the ▁development ▁of ▁the ▁M 1 D , ▁which ▁util ized ▁a ▁simpler , ▁single - ring ▁Spring field ▁Arm ory ▁mount ▁attached ▁to ▁the ▁bar rel ▁rather ▁than ▁the ▁receiver . ▁The ▁M 1 C ▁was ▁first ▁widely ▁used ▁during ▁the ▁Korean ▁War . ▁Korean ▁War ▁production ▁was ▁ 4 , 7 9 6