I just googled (well  duck duck goed anyway) teak spearguns.  What exactly is the hole you are going to drill in both ends for?  I just assumed it was for the spear but  the spearguns I see images of online have the spear sitting in a groove in the top of the gun.   

--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.