I have an M1. You can get military ammunition FMJs with steel cores cheap from the Civilian Marksmanship Program.
It will shoot through 18 inches of oak tree at 200 yards.
A kevlar vest is worthless against it.
It is a one shot, one kill 30-06.
A Level III assault clamshell or a Level IIIa with trauma plates will stop a regular 30-06. Level IV (trauma plate or suit) will stop a .30-06 AP round.
Level IV plate hit by .30-06 armor piercing. Front view:
Rear view
Most SWAT or Assault units have Level IIIa vests with Level III trauma plates inserted at a minimum. The BATF raid guys have been seen parading around in IV plate-carrying suits.
Moral of story - aim for faceplates. Nobody's come up with a practical rifle-proof visor or faceplate yet.
I also picked up some Tommy guns for the first time and realized why mobsters had to be big guys. Damn things were heavy.