Speaking of a barn full of rats, there is a woman in UK who kills them with an airgun with night vision - she is pretty darn good! https://www.youtube.com/user/snypercat
And if anyone wants to know more about hog population control in Texas: http://feralhogs.tamu.edu/
A "fair use" quote from their FAQ page:
11. How hard they are to kill?
How hard are they to kill with what? Very hard with a sling shoot or BB gun! Seriously, most archers shoot wild pigs in the heart /lung region immediately behind the shoulder from broadside or at a slightly quartering away angle. Hunters using firearms are advised to shoot the pigs in the neck or in the vitals (heart/lung region). Preferred rifles for pigs are 25 to 30 caliber. Regardless of the caliber/weapon, shot placement is essential for a clean and ethical kill. Archers typically limit their shots to 25‐30 yards to help ensure a clean kill.
I will add that a .223 soft point in the chest works too, even is it is considered an anemic round.