THEHISTORYOFAR15AftertheKoreawar,theUSarmyhadrealisedthattheirstandardweaponM1rifleandSMGhadbeenbackward.Theyaretooold!!!SotheUSarmystartabiddingtofindanewstandardweapon.ThenEugeneStonerdesignedAR15toparticipateinthebidding.ThisisAR15,5.56mmNATOThisisM14,7.62mmNATOButunfortunately,theUSarmythoughtthattheAR15'scaliberistoosmallthatthesolidercannotuseittoshoottheenemyinthelongdistance.SothearmychoseM14.TheguntheyhandedisM14TheUSarmychosetheM14in1957,thenin1961,theVietnamwarbrokeout....ButintheforestsofVietnam,thesoldierscomplainedtheweightofM14.So,theUSarmybegantofindanewweaponinsuchthepressure.Hearingthisnews,EugeneStonertookhisAR15camebackagain.becauseofitshigh-precision(高精度),lightweightandexcellentergonomics(人机工效),AR15becamethestandardweaponinanunbelieveablespeed.Afterthat,theycalledthemM16AftertheVietnamwar,TheUSarmyalsofoundtoomuchprobleminAR15.Butthistime,theydidn'tgiveitup,theybetterit.First,M16toM16A1M16A1,abettercleaningsystemand30magazineM16In1989,peoplefoundthattheAR15insoldiers'becamedifferentInPanama.Then,weknewtheyareM16A2andM4.M4M16A2ThenewAR15shavestrongerbarrelsosoldierscoulduseitlongerwithoutcomplexcleanandalighterhandguard.M16A2hasalsobeenasignoftheUSsoldiers.LikeM4,thiskindofshortrifleiscalledcarbinegunTheM16A2inSomalia,1993Timepassedby,theopticstechnologyhadimprovedin1990s.TheoldAR15can'tusesomeadvancedscopeintherifle.Butthegovernmentfoundaway-M1913rail.Additontherifleandcarbine.Byusingthisrail,thenewARI5rifleandcarbinearecalledM16A3/A4&M4A1PicatinnyrailAlthoughAR15wasanexcellentdesignandhassomuchimprovement.butitspilotgassystemisgasblowinggassystem.thiskindofgassystemislighterandeasier.Butitwasnotreliable.SotheGermanyH&Kweaponcompanygivesananswer-HK416.TheHK416usesthepistongassystem.Pistongassystemismorereliablebutmoreheavierandmorecomplex.AlthoughHK416ismuchbetter,butUSarmystillusesM4A1.357mmbarrel416mmbarrel508mmbarrelTHANKYOU!ByTenpenny