I've wondered the same thing , Larry. As you know on O/U it's called demiblock rather than chopper. I've had a tough time visualizing how an o/u can be chopper. I see it with bottom barrel where lumps could be integral, but what about top? Is it a dove tail joint which mates top and bottom barrels? Perhaps SGJ can explain this to us since he apparently knows.

Socialism is almost the worst.