I agree with the other slingshot users here. I've taken many squirrels with them. Practice is the key. I was in snowy Buffalo one winter. Work was slow and I had a full basement. I bought a cheap wrist rocket, a few hundred bearings and practiced on pepsi cans. By spring there wasn't an annoying squirrel left in my neighborhood. I've always been fond of squirrel, especially squirrel dumplings.
As a kid I had an uncle who squirrel hunted with them exclusively. He was an amazing shot, I'm not in his league though.
They are handy for getting a meal quietly in a survival situation. I carry one in my bob. The slingshot and 250 ball bearings weighs less than a pound. There are many small critters I wouldn't use a gun on for security (not to mention would blow apart) and I wouldn't risk losing an arrow for them either.
Most squirrels dress out a little less than a pound. Even if I only shot at 50% accuracy that's about 100lbs of meat in a pot for 1lb of gear, not a bad return. Personally, I think I can do better than 50%.
A slingshot was part a careful plan of mine. A few years ago I went for a class in Atlanta. Posted here…
http://www.preparedsociety.com/forum/f23/urban-escape-evasion-22131/
I spent a couple months planning. Scenario… walking home from Atlanta (>250 miles) with what I had with me. I went through all the possibilities I could envision, population centers to avoid, major river systems etc. At the end of the day I came up with 3 pieces of gear that would give me the best chance of eating on a 30 day walk with my skill sets. All 3 totaled less than 5lbs. A rigged trotline, professional grade snares and a slingshot! I already own and use all 3 and now keep them in my bob.