I've got to agree with the .22LR vote--first of all, don't forget to check the used gun rack. I've bought some very good used .22's, all of them inexpensive and very accurate, often with decent scopes on them. One of my friends has a .17 and they are very loud and a missed shot will carry much further [ something to think about when shooting up into trees]. I've not owned a semi-auto so can't comment on them, but every .22 bolt action I've owned, Mossberg, Winchester, CZ, Remington and the Savage/Anschutz I use now, has been a superb squirrel rifle--the Seventeens are impressive, but I don't need that much noise, speed and expense to hunt squirrels----