I've just been thinking about getting a small caliber for them instead of using a big 270. Just want to know what ammo and gun type.
This question will get you 100 different answers that may be wrong. If you are shooting hogs in a trap, get the cheapest single shot 22LR you can find. Then buy ammo. If you are shooting them anywhere else, find a bigger caliber. A rifle is like a tool, and every situation could call for a different tool. Time of day, location, terrain type, shooting style, hog population, hog size, and other variables will all make a difference on what you would want to use for a rifle.
I have shot lots of semi-autos and bolt actions in multiple calibers, but lately have taken a liking to lever guns. If you are a man of few guns, I would think a 357 lever gun would cover a whole bunch of variables due to its multiple ammo options. Every one has their own liking on rifles, but this is just my two cent input.