Best caliber for head shots on small pigs?

We can get within 12-15 yards. Will start with smaller hogs first. So out of a Hatsan Flash which caliber would maximize penetration on a head shot? The Flash is available in .177, .22 and .25.
I'm....
Gunna vote 25 just because of the target🤔🎩🤙
 
Using too small a caliber is Animal Cruelty, the criminal charge. I would go with .30 cal, but .25 may work. Going under .25 would be unethical in my opinion, and illegal.
Clearly you have zero clue what you talking about,..avsolutely zero.
 
Here is a video of a decent young boar taken with a Disco .177 at 17 FPE shooting the Baracuda 10.5gr at 859 fps

That's super messed up. People should not promote that kind of thing. You glorify a lucky .177 shot, and then other people try it.

Think McFly, THINK!
Once again showing you complete lack of knowledge in the subject.
 
As with all of these types of questions it comes down to a couple of points:
- What is the gun and can it be tuned?
- How good a shot are you?
I have my RTI PP 1 setup at 970-980 fps with a 25.39 gr. JSB KO slugs and I have 1.5" grouping at 100 yards which is 53+ FT lbs. At 50 yards its even better. I shoot/practice 3-5 times per week - weather permitting so my shots and focus remain at a known level. I have no doubt that with the right shot opportunity (critical also) that the .22 would drop it instantly.