When I was a kid back in Ontario, I used #4 buck (due to using a single 20 bore) as my jackrabbit (Euro Hare) and fox load in the winter. There were 28 pellets to the 1oz. load and it worked. It did not work well on groundhogs further than about 15 yards - as the gun had a cylinder bore and ground hogs have to be killed on the spot of they get down the hole.
After becoming an adult & doing a bunch of testing, I've come to rely upon 00 or SSG in 2 3/4" mag loading with 12 balls as a work, police then jail guard load. Slugs are also useful, of course in the line of duty.
That said, I never had to use them while working or as a home defense load, but I've oft thought a simple trap load might work better in the home. If the thug is wearing a vest which is highly unlikely here, a double/blow to the chest would most certainly take the fight out, likely even a single shot. With practice using trap loads, you can fire 2 shots that sound like one, when using a pump M870. With a bit of practice, the Mossy does the same. Both shots are on the mark. Yes - the trigger has to be pulled each time. It is much more difficult to hit when shooting that fast using buckshot or slugs due to the increased recoil.
Only a couple of my 'boys' were able to shoot this quickly, but the rest were not slouches in the use of their handguns nor their M870's. The X-Bulgarian Police M1 Carbines we had were a bit of a joke. I think the buckshot threw tighter "patterns".