RE: 22 Cal To Shoot Deer
I do hunt with a .22 caliber rifle, and it works fine.
A 22-250 Remington produces muzzle velocities and energy to rival that of just about any other deer gun. The damage is devastating. I've taken several does with it.
I think, however, that you mean a .22 long rifle or .22 magnum. In that case, it could be pretty inhumane. I'd probably have some pretty harsh words to offer if I ever ran into another hunter using a .22L.R. for deer.
Off the top of my head, I think PA requires the rifle to be center-fire. IMO, the smallest thing available would be a .22 Hornet.
I'd put the low end for whitetail deer at the .223. Anything much smaller might be problematic.