I've done a lot of gunstocks with automotive clears, the most important thing is to clean it well after stripping as there's usually a bit of gun oil absorbed into the wood. I really soak them down with lacquer thinner to get the oil out-maybe there's a better way but this has worked for me, lightly wet the wood with water and allow it to dry to lift the surface fibers so they can be knocked off with sandpaper or a red scotchbrite. If you had the airbrushing done over an original finish hope it wasn't an oil finish? Three coats of clear then sand, repeat untill the grain is full then final sand and rub it out by hand.