The size of the shot is the problem. I used BB shot when I hunted coyotes in Utah. I liked a shotgun better than a rifle in the country I hunted. BB shot rolled them out to 45 yards (full choke, 3" mag, 12 gauge). A hunting partner used a 10 gauge, BB shot, 3.5 mag. This was a 50-60 yard gun. Jus like every other game animal, from rabbits to elephants, it's where you hit them that's the most important. What you hit them with has to get to the boiler works, but you have to hit the boiler to put them down.
Dr Fatguy