I think the concept here would be 1 shell of buckshot and 2 selectively loaded slugs. Right?
You could run it that way. I ran it just like I would with a pistol(http://pistol-training.com/fastest)and just used slugs all the way around. So 2 rounds to the 3x5, reload and 4 rounds to the 8" circle. If you had a shotgun/buckshot combo that patterend well enough, you could probably use buckshot all the way around too. I figure it test the same skill areas. First shot to a low probability target, follow up shot to low probability target, reload speed, and recoil management on a larger target.