There are two ways a rifle or pistol round kills. The first is through pure shock. This happens when a heavy bullet with a large diameter (in relation to the size of the animal) is launched from the barrel of a firearm at a fast speed. Momentum carries the bullet through the target and produces a high degree of shock which damages vitals immediately even if only in the vicinity of those vitals.
The second way a bullet kills is to induce damage to a vital organ through a direct hit or bullet expansion great enough to do damage. Enough damage that the organ ceases to function almost immediately.
Knowing that a 22lr has zero shocking power, no matter what round it is shooting, and the round must depend on accurate placement and maximum expansion to be effective, which round has the best chance to damage vitals and therefore create a quick humane kill?
Yes, a 22 lr will kill a hog if the shot is placed well into a vital area. A segmented bullet that explodes after reaching a vital area will improve the effectiveness of the 22 lr tremendously.
The short answer is with current 22lr bullet designs and velocities the CCI segmented round at around 1600 fps at the muzzle is without a doubt the best 22.lr round for wild hogs. Absent shocking power, the cartridge provides more expansion after entry into the target than any other 22lr round and increases the chance of damage to vitals resulting in cleaner more humane kills.
See the video below of a 50 BMG vs ballistic gel. It is a great example of how shock kills.
Notice that the projectile on these bullets are full metal jacket which are designed for penetration, not expansion. They don't need to expand when they hit the target simply because of the shear force and shocking power they bring. Big diameter, big weight, and fast speed equals shock. When your bullet can blow an animal into many pieces you don't have to worry about bullet placement or expansion into a vital region.
Absent the shocking power, a bullet must damage a vital for a clean kill. If the bullet is normal diameter (normal meaning what we hunt with) and passes through a target and without hitting or damaging a vital, an animal can continue to live for days, or even weeks, and actually bleed to death or experience other undesired means of death. As responsible hunters, we want to avoid this at all costs.
Know that you will never get enough shocking power from a 22lr to kill an animal the size of a wild hog. You may kill a mouse, or a hamster with shock using a 22 lr but that is about it. You can improve the odds of a quick clean kill on any animal by using segmented 22 lr bullets. The CCI segmented bullets at around 1600 fps at the muzzle actually break into 4 pieces immediately after entry into a target. These 4 pieces rapidly expand in all directions greatly increasing damage done to vitals that are nearby and simulating shock to a small degree.
Any other 22 lr bullets like the CCI Velocitor and others, even hollow points will not show much expansion at all. These bullet designs are just not adequate to expand at the speeds they are traveling. I assume that is why CCI developed the segmented line. Finally a 22lr round where bullet performance has been designed to perform at it's actual speed. Proof of that can be seen in the video below. The first shot into the ballistic gel is a segmented bullet, the second shot is a Velocitor.
If there is still any doubt that a wild hog can be quickly and humanely harvested with a 22 lr, check out the video below. This hunter used a Savage FVSR with a tracer bullet, probably a soft point without maximum expansion design. That, and because the camera is mounted directly on the gun is why the shot looks like a big explosion when executed. The shot is well placed in the head as all 22 lr hog shots should be and the kill was sure, quick, and humane.
As with any subject, there are exceptions. The largest feral hog killed on record was nicknamed Hogzilla. It was taken by Chris Griffin in Alapaha Georgia on June 17, 2004. It was alleged to be over 12 feet long and weighed over 1000 lbs.
If you come across a hog this big, I would not suggest shooting him with a 22 lr. Although a perfectly placed shot to the brain would get the job done, I just don't think it's worth the risk of missing that perfect shot. Go home and get a bigger rifle, or bazooka, and try him again.
Although it is more likely a large hog will try to get away when being shot at, there have been instances of humans being charged and attacked by these creatures. This usually occurs when the animal is cornered.
In conclusion, you will never get enough shocking power from a 22 lr to take an animal the size of a feral hog, but you can humanely take wild hogs with it by insuring accurate shot placement and maximum expansion of the bullet you use. You should use the CCI segmented variety. They are sold with different velocity ratings. Make sure you get the fast one, around 1600 fps, to insure adequate penetration before expansion begins. You will then have the perfect set up for wild hogs.