lets not forget that logan pulls his punches when fighting humans and certain meta's so as not to kill or injure...
example:
when he casually elbowed nightcrawler and knocked the wind out of him... NC though he hit him with his full strength and logan responded he could have killed him if he actually elbowed him if he werent actually playing with him or some such...
so an elbow or knee head butt without PIS and best of his ability should break bones, like ribs easy