My method is: remove the stock and repair with a bit of clear low viscosity super glue /epoxy resin. then clamp it (if possible, otherwise don't). Carefully wipe glue with wet cloth. You could also in advance moisten or grease the outside of the stock meticulously to lower risk of the epoxy sticking to it. Inside might tighten a bit (because of the clamping), so light sanding might be needed. tried using wooddust mixed with the resin to match the colour of the wood, but it made the crack darker. A good matching hobby paint (use right paint) job used on car, train plane models etc., does provide far better results.