After reading all the posts on this one, I'd agree that a good 22LR revolver would suit you much more for tree rats. For some years I fielded a Smith M648 22WMR for PD's and ground squirrels. Worked well over a rest, but eventually I scoped it with a Leupold 4X. Worked better, but these things are LOUD!
After a few years a friend just HAD to have it, so I sold it without too much regret. They command premium prices now. I replaced the WMR with a M617 in 4" and still have it to this day. On one trip to MT for PD's, it accounted for 91 prairie poodles when I wasn't at the bench with my rifle.
Since that time, the little 617 has accounted for literally hundreds of ground squirrels here in Orygun. I much prefer the 4" for ease of carry and holster use. The slightly reduced velocity and shorter sight radius doesn't seem to really make much of a difference, and the 4" is just more 'handy'.
Another aspect of the 4" Smith, is that it fits nicely in all my OWB rigs for my M686 which started out as a 6" revolver. Midway had a killer sale on 4" barrels so I snagged one and installed it for a "switch barrel" 357 revolver.
The two four inchers make a handy pair to handle 22LR, 38 Spl and 357 Mag, all using the same OWB leather rigs for carry.
My interest in SA revolvers waned way back in the 70's, so mine now are all DA, which get shot most in SA mode for squirrels for the accuracy it offers when shot that way. Maybe not relative to this discussion, but one of my favorite revolvers is my Smith M651 22WMR, 4" J-Frame with a factory 22LR cylinder for a 'real' convertible revolver. But the OP is wanting a full size, so this is just included for interest.
I'm having a hard time understanding why PA will not allow auto-pistols for squirrels. WTH not? What's the problem? Seems to me a ridiculous rule with no basis in logic. But when do bureaucrats ever consider logic?