I'm not saying I've "seen it all" when it comes to killing feral pigs, but I have seen more than most, and have personally killed more than 700 feral pigs - most with firearms of every conceivable caliber from .22 LR to .357 handgun to 30-30 rifle and up to a .300 Win Mag. I had the rare opportunity to live somewhere for six years where there was literally NO END to the number of hogs I could shoot, so I took it upon myself to experiment - so to speak - with the killing effectiveness of any weapon I could get my hands on.
In those years and through all those hundreds of pigs, I learned a few things.
1) a well placed .22 LR round will drop a 200+ lb. hog in it's tracks
2) a poorly placed 30-06 round will leave a 100 lb. sow running for hundreds of yards
3) shot placement (see above) trumps all else
4) 9mm handguns are not enough to stop a running pig but .40 cal and up will.
5) 6.5x55 Swedes have a well deserved reputation for just "killing" scht
6) .223 is not enough for pigs, for me. If I'm on foot in the brush, I want more gun.
7) FMJ's sail through a pig and they just keep on running
8) In 700 feral Texas pigs, I've yet to shoot one that topped 300 lbs. on a scale, despite all the claims of "huge" feral pigs.
And last but not least, in all those pigs - easily half of which were killed with me standing on the ground - only THREE ever "charged me." All three were wounded and two of the three were backed into a corner in the brush. The other one - I'm convinced - just wanted to escape on the same narrow trail I was standing on. IOW - all the hysteria about feral pigs being "dangerous" is utter nonsense to me until proven otherwise.
So far this year, I've killed two boars that both were easily over 225#. One with a 52# recurve bow that completely penetrated the shield, the heart and the sternum, and the other with a perfect head shot from my 7.62x39 that dropped it where it stood. I am sure many folks would have told me I was under bowed and under gunned in both situations.