Depends on a lot of factors but an AR-15 / AK-47 or other high capacity magazine weapon comes to mind. (Assumes there's no issue in your jurisdiction(s) with a 5+ or 30 round mag).
Either can drop most any hog with a half decent shot. We watched a heli-hog-hunt in Texas: Clearly the vibration and motion affects accuracy but many hogs in a pack went down in short order with a single magazine.
What do you have?
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.50 BMG: 1 Shot 1 THRILL!