RE: Hog hunting with a shotgun...
When u say 'standard shotgun shells' it kind of confuses me...but confusing me is pretty easily done...I'm guessing you're going to be using a shotgun with a regular barrel?
So...if you're using a smoothbore barrel, use 'rifled' slugs. The slugs have to be rifled because your barrel is not, and, you need the spirals to provide stability for the in-flight slug to be accurate. These come in 2 3/4" or 3". I don't think that matters much if your shots are going to be close. The main thing is that different slugs don't seem to hit the same point of aim, so you'll need to buy 3 or 4 different types and try them to see which your gun shoots accurately.