Lots of pigs are taken each year here in Aus with double rifles.
I regularly hunt for quality boars in high country in far west New South Wales, out on the flat country of outback Queensland, and up north in the creeks rivers swamps and waterholes of Cape York.
My favourite hog slayer is a 400-350 which works real well in all those locations.
For big boars in thick cover however, something like a 470 or 500 nitro is just the ticket!
The double rifle is just perfect for hogs in thick bush IMO.