To dispell the hole dulling your blade once you hit bone rumor... yes it will dull ever so slightly but when I was a kid we built a machine that would shoot a sharpened #2 pencil through a 2x4 and as long as it is done fast enough the pencil remained sharp! Also ribs are rather weak bones that provide little resistance to blades but a shoulder might dull it more. In our case the arrow would be moving so fast that the actual dulling or bending of the blades wouldn't appreciably occur!