I bought a Parker VHE 20ga shotgun at a DEEP discount because the toe had be split off and lost. This is a gun worth somewhere around $5500 on the market. I cut the surface of the damage area flat and square to the side of the stock. Next I found a piece of walnut very similar in grain and made up a matching piece with a tenon on the mating surface to fit into a slot I cut into the butt stock. Make sure these fit accurately on the edges by filing a slight draft on the added piece edges they will clamp tightly at the edges. Titebond glue and rubber tube clamp. Finish the addition down to proper profile stain and finish it to match the rest of the stock. Hand rub on a thin varnish finish without running it onto the original stock until the very last coat. The repair has lasted 30 years and because I colored the line and finish with some lamp black mix the whole thing is now invisible. I got the gun for less than half of its value. There are professionals will do this work for you for a modest fee. Better if you find the missing sliver of wood though.