It is amazing what you can do with a regular old semi-auto 12 gauge with the plug removed, I have even used my over-under when it is what I had at the time. I recommend buckshot from bow blind distance. You will be lucky to get off five shots before all the pigs have disappeared from view. I have done this several times, fun.
We have timed pigs and how fast they respond. They move 10-15 feet in the first second after the first shot, and then all shots are all moving targets. In two seconds they are mostly clear of the feeder area.
I like skinnerback's shotgun, that would be awesome for running down pigs across a field in the Gator. I have run out of shots doing that before.
I've done this with a pump 12 guage. I got off three shots and had 3 pigs dead and multiple blood trails that I didn't bother following. I went out this morning and got 2 with my 357. IME, once we get after them pretty hard, they get the message and go find a different corn feeder. We just have not hunted them hard this year yet.