[Buzzbee]

If it's not too deep, steam from a cloth iron over a wet towel will raise light dents but make sure it does not have urethaen type of finish as steam can cloud it up. Your approach with steam should be slow, specially if the wood is kiln dried, you can easily over raise the surounding area creat ripples in the stock.

 

[Buzzbee]

If it's on a field gun, I would leave it alone, you'll get more dings on faster than you can repair it, so why bother.
However, if you must, shellac sticks is another option you may try. Natural light source is important when working with shellac to assure best color match, it's not hard but it take some skill to work with, touch-up with oil afterward most likely will be reqiired.
You can get it from Brownells or any fine funiture/ wood working places.