It isn't buckshot, but the first 3 rounds in our HD shotgun are Zanoletti Double Impact. This ammo consists of 2 shot cups that each holds 1 oz of BBs.
I believe the round was designed for longer range large bird hunting. The first shot cup is supposed to open at about 30 yards and the second at 100. In reality, the first cup starts to open in just a few yards. For HD distances, say 10 yards, you will get a small spread of BBs from one shot cup, plus the residual of that cup of loose BBs and then the second unopened cup of 1 addition ounce of BBs that will perform much like a slug since they are still contained in the shot cup.
I find the ammo probably isn't great for longer range shooting if you want a consistent pattern. At 50 yards, the opened shot cup will pattern very irregularly in a 10 foot diameter area and have some flyers well outside the main pattern. The second shot cup by 50 yards is still closed.
After the Zanoletti, I have 3 rounds of Federal reduced recoiil 00 Buck. Carried on the stock are 5 more rounds of Brenneke slugs.