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I've only killed 3 hogs, but had a neighbor who hunted them as though they owed him money. From all of the articles I've read and the guides I've hunted with, the 30/30 is probably among the smallest cartridges that will get the job done consistently, presuming you keep the distance to 150 yards, or so, and of course your shot placement is good.
Personally, if I didn't have a gun and was planning to buy one specifically for wild hog huntin'...it wouldn't be a 30/30. I'd look for a long action caliber such as a .270 Winchester, 30-'06 or 7mm Remington Magnum. Cartridges in this class will give you longer range, more power and better penetration. Two of the guides I hunted with said they absolutely want an exit wound because very few hogs drop when hit so they will need to be tracked, most likely. One hole going in isn't going to leave much of a trail, usually, but the one going out tends to be a little bigger.
If you aren't up to the recoil of a standard length cartridge a 308 Winchester would do the job, as would classics like the 7x57 and 6.5x55 (or their respective modern equivalents, the 7mm-08 and 260 Remington). If you keep the range less than 100 yards, you could go with a 44Mag in a lever-gun or maybe get you a Thompson/Center Encore in 300 Win Mag. and shoot 'em at 400 yards...the possibilities are endless!
I'm sure our good buddy Tang, (forum member) will be recommending something based on the 50 BMG case in a little while...that might be a little bit of over-kill, but hogs are tough critters and the truth is, you can't really kill somethin' TOO dead.
Be prepared to get about 100 responses to your question, with everything from a 22LR to the ear all the way up to a .458 Mangle'm for those stem-to-stern shots. If you stick with the first three I recommended, you won't go far wrong.
Jason