▁during ▁engag ements ▁and ▁not ▁particularly ▁useful ▁when ▁heard , ▁as ▁other ▁squad ▁members ▁might ▁have ▁been ▁nearby ▁ready ▁to ▁fire . ▁Due ▁to ▁the ▁often ▁inten se ▁de af ening ▁noise ▁of ▁combat ▁and ▁gun fire ▁it ▁is ▁highly ▁unlikely ▁any ▁U . S . ▁serv ic emen ▁were ▁killed ▁as ▁a ▁result ▁of ▁the ▁ping ▁noise ; ▁however ▁some ▁soldiers ▁still ▁took ▁the ▁issue ▁very ▁seriously . ▁ ▁Gas ▁system ▁ ▁Gar and ' s ▁original ▁design ▁for ▁the ▁M 1 ▁used ▁a ▁complicated ▁gas ▁system ▁involving ▁a ▁special ▁m uzz le ▁extension ▁gas ▁trap , ▁later ▁dropped ▁in ▁favor ▁of ▁a ▁simpler ▁d ril led ▁gas ▁port . ▁Because ▁most ▁of ▁the ▁older ▁rif les ▁were ▁retro f itted , ▁pre - 1 9 3 9 ▁gas - t rap ▁M 1 s ▁are ▁very ▁rare ▁today ▁and ▁are ▁pri zed ▁collect or ' s ▁items . ▁In ▁both ▁systems , ▁expand ing ▁g ases ▁from ▁a ▁fired ▁cart ridge ▁are ▁di vert ed ▁into ▁the ▁gas ▁cyl inder . ▁Here , ▁the ▁g ases ▁meet ▁a ▁long - stroke ▁p ist on ▁attached ▁to ▁the ▁operating ▁rod , ▁which ▁is ▁pushed ▁rear ward ▁by ▁the ▁force ▁of ▁this ▁high - press ure ▁gas . ▁Then , ▁the ▁operating ▁rod ▁eng ages ▁a ▁rot ating ▁b olt ▁inside ▁the ▁receiver . ▁The ▁b olt ▁is ▁attached ▁to ▁the ▁receiver ▁via ▁two ▁lock ing ▁lug s , ▁which ▁rotate , ▁un lock , ▁and ▁initi ate ▁the ▁e jection ▁of ▁the