Bee-are we to assume that when you say "instrument" you are referring to musical instruments? there might be a difference in the answers you get.
   The guitars I saw in Korea years ago (about30) were barely worth using to bludgeoning--I certainly hope they are made beter nowadays.
However,I digress. I've long thought that a musical saw might be interesting to use when the need arises to bludgeon an assailant.