I shoot a .22 reset target almost everyday at 50 yards. which is a 2 inch bull. so ya I think I'd be fine on tree rats. Keep practicing you'll get the hang of it.
-Jake
I have hit a couple at that range with my 597. It is entirely possible-better odds with a good rest obviously. I love my 597-I put a 4x32 on it a while back and it's my go to gun for small game. Great shooter.
i can put an entire clip of 22s in a squirrel silhouette, off hand, at 60 yards. if 40 is tough, rest off your knee, or use a tree, or even a mono-pod. the farther the shot, the more fun in my book