Survival Grips has an interesting product. It is a vertical grip with a knuckle duster integrated into the grip.
The grip is polycarbonate. The Finger Guard is made of Aircraft Grade Aluminum 6061 T-6. The grip will fit on Mil-STD-1913 or Picatinny Rail.
The knuckles are removable for what ever dastardly deed you need to use these for. It doesn’t pique my interests but perhaps it is something you need for your zombie prepper rifle.
For those interested in purchasing one, they can be found here.