I wrote a body-part-detection once for my multiplayer western shooter, because the model hull is not being updated through animation cycles.

This "precise_shot.wdl" uses bones, too.
It makes a mathematical check whether a shot from a certain point to a certain direction passes a bone in a certaint distance or not.

Values like target vector and hit bone can be accessed, but you have to cross-check with a trace if there was soemthing in the way and call the function itself through a you=ent_next() loop for each entity.

It worked quite well, here's the thread:
precise_shot for ego shooters

The demo is not online any more, but the script file is.
Within the file there is a comment-description on how to use it (if still needed). ^^