You may hunt small game with a centerfire. I use to do it. I would recommend using normal loads that maximise accuracy and take only head shots. Keep in mind you must have a background to shoot into. That bullet can go 5 miles. I would hunt along ridgetops always shooting down towards the ground. A 100 yd headshot on a squirrel gives you a good feeling. I used a light barrel .222magnum with double set triggers and a 12x Luepold. Worked great after the leaves are gone. I also hunted where some cornfields bordered a mountian and set up in a fence line about 180 yards from the edge. I was shooting into a mountian and had fun picking fow squirrels off. Have fun, keep it safe.
I thought it had to be .22 and smaller and a rimfire, but the way it is worded it may be just handguns need to be rimfire. They do have a note about the caliber restrictions do not apply to woodchucks, but that note does not say about rimfire. It could be a little more clear.
The way I read it is a centerfire round of 22 cal or less.
I at one time used a lot of different downloaded rounds for squirrel. My 30-06 and 308 loads for squirrel became inaccurate at 30 yards but were quite good at 25. A lot of my "squirrel guns" became illegal when the Game Commission instituted the 22 cal rule. I got a lot of funny looks with my squirrel guns but it gave me a lot of extra time with my rifles. Cast bullets were the answer in a lot of the different rounds.
Used to enjoy hunting small game with my big bore revolvers, loaded down with cast bullets. Used to enjoy handgun hunting for turkey in the fall, would love to be able to hunt small game with my scoped .22 semi-auto target pistols like I could years ago in anti gun CT. But nope. The PA Game Commission giveth, and taketh away....