lets ▁must ▁be ▁produced ▁to ▁a ▁high ▁standard , ▁as ▁surface ▁imper fe ctions ▁can ▁affect ▁firing ▁accuracy . ▁ ▁The ▁physics ▁affect ing ▁the ▁bullet ▁once ▁it ▁leaves ▁the ▁bar rel ▁is ▁term ed ▁external ▁ball istics . ▁The ▁primary ▁factors ▁affect ing ▁the ▁aer od ynam ics ▁of ▁a ▁bullet ▁in ▁flight ▁are ▁the ▁bullet ' s ▁shape ▁and ▁the ▁rotation ▁im part ed ▁by ▁the ▁rif ling ▁of ▁the ▁gun ▁bar rel . ▁Rot ational ▁forces ▁stabil ize ▁the ▁bullet ▁gy ro scop ically ▁as ▁well ▁as ▁aer od ynam ically . ▁Any ▁asym met ry ▁in ▁the ▁bullet ▁is ▁largely ▁can ce led ▁as ▁it ▁sp ins . ▁However , ▁a ▁spin ▁rate ▁greater ▁than ▁the ▁optim um ▁value ▁adds ▁more ▁trouble ▁than ▁good , ▁by ▁magn ifying ▁the ▁smaller ▁asym met ries ▁or ▁sometimes ▁resulting ▁in ▁the ▁bullet ▁expl oding ▁mid way ▁in ▁flight . ▁With ▁smooth - b ore ▁fire ar ms , ▁a ▁spher ical ▁shape ▁was ▁optim um ▁because ▁no ▁matter ▁how ▁it ▁was ▁orient ed , ▁it ▁presented ▁a ▁uniform ▁front . ▁These ▁un stable ▁bul lets ▁t umbled ▁er rat ically ▁and ▁provided ▁only ▁moder ate ▁accuracy ; ▁however , ▁the ▁aer od ynamic ▁shape ▁changed ▁little ▁for ▁centuries . ▁Gener ally , ▁bullet ▁shapes ▁are ▁a ▁comprom ise ▁between ▁aer od ynam ics , ▁interior ▁ball istic ▁necess ities , ▁and ▁terminal ▁ball istics ▁requirements . ▁Another ▁method ▁of ▁stabil ization ▁is ▁to ▁place ▁the ▁center ▁of ▁mass ▁of ▁the ▁bullet ▁as