Realistictly, even a .22 can take down anything if you hit it right :wink:
If you have a good head shot on something, a .32 should do the trick. Id think it capable of killing any small critter or varmint. Not sure about getting up to coyote size. On a broadside shot, Id imagine the ball would enter and penetrate the lungs, not sure if it would exit though.
Airguns nowadays shoot pellets close to 2000fps, even the .22 and .25 caliber pellets get like 1000fps. Id imagine the energy needed to pass an arrow through a critter would be different than the energy needed to pass a round ball, since the arrow is propelled from a single, small position (the nock), whereas a round ball is pushed from the whole rear-side. Plus, the actual point of penetration of an arrow is smaller than that of a round ball, since the point of an arrow is smaller. So, all that energy is focused into a smaller area, which gives it good penetration. A round ball hit its target with the full front-side, so the energy behind it is spread over the whole area.
Primitive bows have a draw-weight of roughly 30 pounds on average. But, there have been flint/rock arrow heads found that can fit on your finger they are so small (usually called "bird points" because they were thought to be used for hunting birds.) Testing blood left behind on these points revealed they were actually used to hunt big game (deer and elk) and after testing replica points, arrows, and bows on deer, the arrows had excellent penetration, usually passing through the deer or stopping underneath the skin of the opposite side. The reason behind it being that the low amount of energy released from the bows is focused onto such a small point, it gives the small point good penetration. So heres your
ff info :idunno: