Traditional finishes turn darker with age, and the older guns used a better grade (denser, darker) of walnut. Today, stocks are mostly beech, unless you pay extra for genuine walnut. And even then, it's a lighter, less dense walnut, unless they offer an option of a really expensive walnut.
I've had good luck refinishing modern walnut stocks with some Brownell's "military walnut" stain, which darkens and adds a nice red tinge. And a nice tung or linseed finish looks traditional, even if not too durable. For "durable", you have to go with the modern plastic finishes.