My question would be how mant shots would one's shoulder last?
At 4,000 FPS for a 450 grain slug. I wonder if one used a sabot if one could get escape velocity and one's personal space program? Maybe that will take a 37mm necked down to .17 cal.
Stay well - Stay safe - Stay armed - Yorktown
I think I would not shoulder the 20mm/.50, but crank it into a very large vise, adjust it via a closed circuit camera scope, and fire it remotely.
I think that's probably the only shoulder arm in the world that really deserves to be called a single-shot. I'd sure want more of a shoulder pad on mine!