Hello from Germany!
The most used calibers for hunting feral hogs here in GE is the .30-06, many hunters take also the original german cartridge, the 8x57 IS Mauser. Further more a .308 with heavy bullet is also good. The point is not the bigness of the cal. but the shotplacement and distance. The anatomy of a hog is very different to deers. In most cases you have to aim in the center of the hog's body to get a deadly hit. Many hunters here in GE aim behind the ears and hit in many cases the backbone, but in a bad way, so you have a wounded escaping hog. Searching such an animal is not much fun both for the hunter and the dog.
On drive hunts slugs are often used.