Even a 1oz slug won't always do it
Back in my young period, I hunted in Swampeast Georgia. Whitetails were the game of choice but feral hogs were fairly common. One day my friend Bobby Troupe and I were out scouting deer sign in his old CJ Army surplus Jeep. Suddenly Bobby threw on the brakes and says "They is a little gilt down there." (Note: A gilt is a young female pig)
With that said, he produces a Colt Woodsman .22 and I picked up his .223/20ga Savage OU. Bobby carefully aims the .22 down toward the swamp and squeezes off a round. At this point I had yet to see a pig. As soon as the pistol went off, all he!! broke loose! Pigs went EVERYWHERE! Big hogs, little hogs, piglets, you name- it there were pigs gone to seed. I picked out another gilt as it crossed the road and killed it with the .223.
By the time the dust cleared up, we had 2 pigs down. The one Bobby shot turned out to NOT be a gilt after all. It was a sow. A big sow weighing somewhere around 250 lbs. Bottom line is it took us gol dang all night to get them butchered out. Odd thing was, Bobby killed the sow with 1 round from the .22 and try as we might we never found a single hole in her hide.
That sow was just impossible to eat. I don't care what you did to that pork, it tasted just like my boots flavored up with pine tar and fungus cream. We finally had a BBQ and fed it to the Marines stationed at NAS Gylnco and even they couldn't eat it until after they got drunk.
The question is not how much gun you need to kill a hog but why on earth would you want to kill one of them nasty things to start with?