▁constru ctions ▁depending ▁on ▁the ▁intended ▁applications , ▁including ▁special ized ▁functions ▁such ▁as ▁hunting , ▁target ▁shooting , ▁training ▁and ▁combat . ▁ ▁Although ▁the ▁word ▁" bullet " ▁is ▁often ▁used ▁incorrectly ▁in ▁col lo qu ial ▁language ▁to ▁refer ▁to ▁a ▁cart ridge ▁round , ▁a ▁bullet ▁is ▁not ▁a ▁cart ridge ▁but ▁rather ▁a ▁component ▁of ▁one . ▁ ▁A ▁round ▁of ▁am mun ition ▁cart ridge ▁is ▁a ▁combination ▁package ▁of ▁the ▁bullet ▁( which ▁is ▁the ▁project ile ), ▁the ▁case ▁( which ▁holds ▁everything ▁together ), ▁the ▁prop ell ant ▁( which ▁provides ▁the ▁majority ▁of ▁the ▁energy ▁to ▁launch ▁the ▁project ile ) ▁and ▁the ▁primer ▁( which ▁ign ites ▁the ▁prop ell ant ). ▁ ▁This ▁use ▁of ▁the ▁term ▁" bullet " ▁when ▁int ending ▁to ▁describe ▁a ▁cart ridge ▁often ▁leads ▁to ▁confusion ▁when ▁the ▁components ▁of ▁a ▁cart ridge ▁are ▁specifically ▁referred ▁to . ▁ ▁Bul let ▁sizes ▁are ▁expressed ▁by ▁their ▁weights ▁and ▁diam eters ▁( re ferred ▁to ▁as ▁" cal ib ers ") ▁in ▁both ▁imperial ▁and ▁metric ▁measurement ▁systems . ▁For ▁example : ▁ 5 5 ▁gra in ▁. 2 2 3 ▁cal iber ▁bul lets ▁are ▁of ▁the ▁same ▁weight ▁and ▁cal iber ▁as ▁ 3 . 5 6 ▁gram ▁ 5 . 5 6 mm ▁cal iber ▁bul lets . ▁ ▁The ▁bul lets ▁used ▁in ▁many ▁cart rid ges ▁are ▁fired ▁at ▁m uzz le ▁veloc ities ▁faster ▁than ▁the ▁speed ▁of ▁sound ▁—