The DOD backed off from their short lived policy of destroying all brass from firing ranges.
That is the main reason why 223 and 308 ammo became so scarce. The brass was not being recycled into civilian hunting rifles.
Potato guns have pretty good knock down potential.
But I like the bean shooters that shoot multiple beans with one CO shot.
Think about a golf ball at 2600fps. If a tennis ball can be launched at 300 mph and penetrate plywood, what would a golfball do at 25yards? White beans in a 12 ga. shotgun shell are a real deterent also!