what we call whistle pigs are more commonly called gound squirrels or "pot guts" over in the tenessee area. Right now, with the exception of the last few days, its been real dry so all the green vegatation they eat during the spring is now tuning brown.
You guys mught not believe me, but these animals are very cannibals by nature. Even when they have green vegetation to eat, they will still eat dead ones of roads and drag the dead ones you shot back to their burrows.
Even still, as cannibalistic and disease ridden(they can carry/transmit Rocky Mountain spotted fever, rat bite fever, Tularemia, Chagas’ disease, adiospiromycosis and encephalomycarditis and the Bubonic plague to humans, if dead ones are handled) as they are, i dont like using .22lr even with HP's, because more often then not, they suffer. There have been countless times ive hit them in the side and they run around and go down a hole to die probably 1/2 hour later. Head shots will do fine, but it takes a good shot to hit a head the size of a quarter at 40yds while standing.
Personally, i would use any round that has a ballistic tipped bullet. I used to use my marlin model 60 .22mag with CCI ballistic tips and they work very well. Now i reload for my Savage model 10 FP and use 110gr. Hornady Vmax's in my .308. The .22mag would tear them up, unlike hp .22lr's, and my .308 will throw chunks of them 20ft in the air.