the sinew and tiller is the key,, also,bows in that weight range seem to be able to bend further,, I think as they get heavier the is more chance of failure,, but that is just one of my crazy thoughts based on pure speculation,,
![Smiley :)](http://www.primitivearcher.com/smf/Smileys/default/smiley.gif)
the width to poundage ratio or something like that,