I've done battle with black walnuts in the past - my in-laws has a small grove of mature trees on their farm in south-central Michigan. A big part of their harvesting strategy was to spread the walnuts in the driveway and run over them for a while. Then use a vice to get a controlled crack.

Each fall I would bring a gunny sack or two to parent's place so they could spread some on their driveway...

I had some juvenile black walnut trees (about 4-6" caliper) on some property in the Upper Peninsula of Michigan, but never had a harvest.

When I first stumbled upon the hickory nuts, I first thought they were walnuts (until I picked one up).

-aj