hilbily:
While Mark thinks walnut should be stained I feel I owe it to a builder who's working with walnut to say, before you do any staining but after you have given the stock a good sanding to make it smooth, take your stock and a wet washrag out into the sunlight.
Use the washrag to dampen the wood and look at the colors and grain contrasts.
This wet wood is exactly what the wood will look like after you apply the finishing oils without any stain at all.
If there are light areas then consider staining the wood but I'm betting that your stocks walnut will look great without any stains at all.
IMO, walnut is already so dark that any stains that are added to it will just cover up all of the nice grain pattern and make it look brown or redish brown without any interesting patterns.