I've never used epoxy resin, and I imagine working cured epoxy is pretty hard as well, how did you shape it? 
A belt sander, oscillating sander, ROS sander and some hand sanding.   I have managed to throw away several butt stocks because of not paying attention on the belt sander.  As soon as I try to short cut or speed up the process I really do end up with a piece of scrap.  I would guess it takes me about 3 hours to complete a butt stock once I have a blank.
But time isn't an issue, I've got all the time I have left  ‹(•¿•)›