Some 5.56 rounds, like M855 and the newer one will defeat some III & III+ plates.
I haven't seen any 5.56 rounds that will defeat Level IV plates.
Why would a shooter waste a shot, of any sort, on anything that looks like a vest/armor/,etc. Head shots or maybe belly or thigh shots will change the attitude of the miscreant in jig time? If one can’t shoot one might want to avoid starting a fight.