Quote Originally Posted by Jim Watson
the cocking knob has a large dovetail cut in it
That is for a cocking piece peep sight. It got the aperture as close to the eye as possible, like a tang sight on a lever action. But folks worried about wobble in the bolt and the receiver sight pretty well took over in later years.
one such sight is the Lyman 1A, they come up on ebay with some frequency.