They must love their hogs on Fort Sill, because even with buckshot a pig still has a chance to run off and bleed(and/or breed) later.
I shot at a good pack of razorbacks(They were as close to the school logo as I saw it, just in black and gray). Ran straight through my buckshot. Didn't stop at all. Sunset came before I could track them down, and that ended my day. I found their bones the next day thinking that I didn't hit any of them, I did, it didn't stop them. Shotgun was a Mossberg 935, the turkey model in Mossy Oak Obsession(not a bad gun), shotshells were 00 buck in a 3 1/2 inch magnum shell.
For a shotgun I won't recommend anything less than 000 buck, but I will say that you completely skip the buck and just go straight to slugs. I know you just spoke of the legalities, this is my overall personal opinion.
Buckshot, and anything less is worthless on a hog, in my opinion. For something that size, with their ability to move after being shot, you're looking for quick, clean kills with as big a bullet as you can get. You need power plus penetration.
I will let you on to a little secret. Bows. They're was a guy I knew of who hunted in a different area then all the other hunters who carried firearms around, and he only carried a bow.
He was taking 2 hogs a week.