Why the heck would you "dig the foam out" after filling the butt with it ? The poly foam is NOT supposed to become rock hard....and that doesn't matter anyway. Filled with the cured foam, the butt stock is much more rigid than before - as rigid as it ever needs to be.
If you insist that it be hard as a rock....I would suggest filling it with concrete. Then, you'll get that "rock hard" feeling you want.....
