RE: .17 HMR Squirrels?
i've always used .22's and have had no problem. i use hollowpoints out of mine and in my opinion they do maximum damage with the least amount of meat loss. no matter where you hit them. like someone mentioned, head and neck shots are preferable but when only the body is present or it is scrambling then i will take that shot. i have never had a problem with the hollow points, they've always taken them right down. and i dont think i'd be worried to much about stray bullets. a .22 will on average go at most a mile and thats in an open area. add some woods and i doubt it will go far. be sure your not firing towards towns though just to be safe. if this is just backyard plinking were talking about then i'd invest in a good airgun that shoots pellets. .177 should suffice with an fps upwards of 650.
good luck and good huntin'