Bone black should be in the last top coats only. NOT in the first applications of finish.
I would stain and oil finish the gun. When the first coats are dry, put more coats on top that are mixed with the bone black. This makes the whole gun darker. Then rub back the finish to reveal the lighter finished wood underneath, and leaving dark in the low wear areas. You can use Burnt umber with a touch of bone black in it, so it's not so severe.
DON'T use bone black and oil on raw wood. Your stock will be black, and no way to rub it back without removing wood.