The most effective bulletproof armor only cover >.38 caliber rounds, and M4A1 and other weapons of that caliber are something like .45 caliber.
Ninja training plus a Katana.
You are not the demoman. That will not work.
more often than not, a 7.62 fmj round is going to go through you whether you are armored or not.those things go right through walls and keep going.
lolwatspecify 7.627.62x39 mm makes neat little holes at close range with no pinwheeling aka less damage.7.62x51mm NATO will turn you into meat chunks.
You're dead either way. The NATO round will just have a huge exit wound, massive internal bleeding, and obliterated organs.