If this gives you a warm and fuzzy feeling, when McMillan beds one of their stocks for a customer, they fill that space and hand cut it with a die grinder and a single flute cutter ( pencil grinder ). It gives the rifle a very custom fit and look. That's where I seen it done with Marine Tex.
If you want to add a little density for extra weight, you can mix some sand in with whatever epoxy or resin you decide to use. Did it on my Savage AccuStock and gained about 2 lbs. Really made a difference once I got it to the range and it was great for 200 rounds while I saved for a new stock. No doubt it would have held if I kept it.
Mix up some resin with baking soda. Clay/tape up a dam to keep it from oozing.
Pour, go watch TV, come back and begin the task of knocking it out the way you want it.
Baking soda ROCKS for this kind of stuff. If you have pin holes (and you will) don't sweat it. Pack some more soda in the holes and use thin CA (superglue) available at any hobby shop that deals in RC planes/cars. Just be careful and have it ventilated.
Thin CA and soda react almost instantaneously and the fumes are like a face full of mace.
We do this stuff 6 days a week at my shop. Works awesome and is dirty cheap/fast.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hero's machine</div><div class="ubbcode-body">The nice thing about baking soda that never gets mentioned, if you mix your resin so hot it bursts into flames......the soda puts it out. It's a win-win! </div></div>