Looks like what I would call flamed. I don't think you could find a burl large enough to make a gunstock that long very easily. Burls are growths on the sides of trees, not a type of wood grain exactly. You might have one side of a tree that has a burl growth long enough to get a rifle stock, but the grain is crazy interlocking swirls, and often has bark inclusions.
This is what I would call "flame", aka quilted.Curly, aka Tiger striped-Ron