We always loaded slug, 00, slug. Thought was 1st shot (slug) standing, 2nd shot (00 or 000 buck) moving/running, 3rd shot (slug) is last chance and most likely won't be close. Only time we are 00 only is when we are stalking in the woods and expect a deer either escaping or creeping away. BTW, I normally hunt with my AR15 in 7.62x39 and don't miss.
Makes good sense...Federal buckshot with the flight control wad holds the tightest paterns i have seen..