Mmm,, for black walnuts a sledge hammer and a piece of railroad iron would work better !! :
My above "pictured" nutcracker will "crack" those black walnuts ... just s fast as you can place a walnut in the lower jaw and crank the handle down. And it will never "crush" one unless you crank the handle 2 or 3 more times on the same nut.
Black walnuts hulls are tough to "crack" ..... but
not half as tough as a Butternut (white walnut) hull.