An AR pistol with green tips. If u could conceal under a vest with a shoulder sling or in a backpack. Some green tips would go right thru.
You don't need the green tips. The itty bitty coathanger thickness short steel rod is fairly inconsequential and if you are relying on it for penetration, then like real AP ammo through hard armor, the mostly only the steel penetrates. That is why a .50 BMG AP round doesn't put a full .50 hole through a steel target. You get a hole a bit bigger than .308...which is the size of the steel core inside the .50. That is based on a couple folks shooting one of my MGM targets with AP ammo by 'accident.'
A regular 55 gr fmj will go through just fine.