I'm with Dave (TOF) on this one. Don't even bother to remove the loose stuff...mix up some AcraGlas (Brownell's) with some black dye, drip it into the cavity until you have a puddle above the stock's surface, and cover it while wet with a piece of clear packing tape. The tape will hold it so it doesn't run, and keep a nice bulb of the expoxy above the surface of the stock. When it has cured, remove the tape and sand it flush. It'll look great.