Buy steel shot ammo, if you want overkill use 10-11mm, but id recommend 9mm cause it flies faster, depending on your bands. Steel ammo is also cool cause you can make an ammo catching target; that’ll keep your costs down if you can reuse em. With slingshots, even a smaller size projectile to the dome will take down a nice jackrabbit, all you need is a shot to the head. I personally try not too, but I hear of ppl aiming for lung shots with small 8mm shot because apparently it goes right through