ers , ▁the ▁problem ▁was ▁solved ▁to ▁a ▁large ▁degree . ▁ ▁T rac er ▁r ounds ▁can ▁also ▁have ▁a ▁m ild ▁inc endi ary ▁effect , ▁and ▁can ▁ign ite ▁fl amm able ▁subst ances ▁on ▁contact , ▁provided ▁the ▁trac er ▁comp ound ▁has ▁started ▁burning ▁and ▁is ▁still ▁burning ▁on ▁impact . ▁ ▁History ▁▁ ▁Before ▁the ▁development ▁of ▁trac ers , ▁g unn ers ▁re lied ▁on ▁seeing ▁their ▁bullet ▁impact s ▁to ▁adjust ▁their ▁aim . ▁However , ▁these ▁were ▁not ▁always ▁visible , ▁especially ▁as ▁the ▁effective ▁range ▁of ▁am mun ition ▁increased ▁dram atically ▁during ▁the ▁later ▁half ▁of ▁the ▁ 1 9 th ▁century , ▁meaning ▁the ▁bul lets ▁could ▁impact ▁a ▁mile ▁or ▁more ▁away ▁in ▁long ▁range ▁area ▁fire . ▁In ▁the ▁early ▁ 2 0 th ▁century , ▁am mun ition ▁design ers ▁developed ▁" spot light " ▁bul lets , ▁which ▁would ▁create ▁a ▁flash ▁or ▁smoke ▁pu ff ▁on ▁impact ▁to ▁increase ▁their ▁visibility . ▁However , ▁these ▁project iles ▁were ▁de emed ▁in ▁viol ation ▁of ▁the ▁H ague ▁Con vent ions ▁prohib ition ▁of ▁" expl oding ▁bul lets ." ▁This ▁strategy ▁was ▁also ▁useless ▁when ▁firing ▁at ▁aircraft , ▁as ▁there ▁was ▁nothing ▁for ▁the ▁project iles ▁to ▁hit ▁if ▁they ▁missed ▁the ▁target . ▁Design ers ▁also ▁developed ▁bul lets ▁that ▁would ▁trail ▁white ▁smoke . ▁However , ▁these ▁designs ▁required ▁an ▁excess ive ▁amount ▁of ▁mass ▁loss ▁to ▁generate ▁a ▁satisf actory ▁trail .