I've read every message posted so far, and to my surprise, even though many claimed to be "old school", not one mentioned the most practical and useful firearm for tree rat hunting, the Savage #24. This was first, and my first one also a .22 lr over a full choke 410 barrel, later with many different combinations. I started my sons with that same little .22/410, and have added to it with a .22 wrm/20 guage, a .223/20 gauge, a 30-30/20 gauge, a .357/20 gauge and the last a .17/ 20 gauge. Each and every one came with a groved .22 scope attachment point or drilled and tapped for a better scope mount.
Several of these I picked up used at yard sales, although the last two did cost like rip, but still less than a new pump shotgun. A decent long eye relief scope is very necessary, to keep from getting cut by the scope from shotgun recoil.
The stiffness of the rifle barrel attached to the larger shotgun tube seems to enhance accruacy, and every one I have owned would shoot better than the operator could.
By moving the selecter, the operator shifts from rifle to shotgun barrel, and has instantaneous choice of which he shoots, I think i tis a great system for anyone.