I've seen a .357 take a medium size hog (130lb) right to the ground with not even a whimper from him and I've also had a little 100lb sow take a round thru the shoulders (destroyed both front shoulder roasts ) and it never slowed her down....................took slitting her throat and a .22 in the ear to make her finally lay still. So a LOT just depends on the particular pig & what kind of mood he is in that day.

Like ths78 said, a 180gr hard cast bullet IS a good choice if you load your own, If you use factory ammo, then the Winchester Supreme load using 180gr Nosler Partitions will be your best bet.

One word of caution - treat those guys with respect, cause they can tear you up before you can bat an eye. So fire, and be instantly ready for follow up shots.