I'm no expert, but those BB rounds really do seem like the best round for a Bulldog. That I know of, the Bulldog just doesn't get that large projectile moving fast enough to expand properly. BB's approach of using a large, hard slug to do as much soft tissue damage as possible at the speeds a short barrel will provide.
Sadly...I waited too long and it seems that Midway no longer carries that round at all, not even backordered. It lists it as "discontinued"...many other places show it as out of stock.
Buffalo Bore shows it as "in stock"...at a whopping $40/20 (YIKES).