A friend of mine put a scope on a 20 gauge o/u for picking squirrels off around his birdfeeder, odd looking but effective! My .410 of choice for red squirrels invading the yard is this one: http://www.michigan-sportsman.com/ph.../IMG_04142.JPG
It also shoots slugs for the invading woodchucks!
Here is my original .410 slugger: http://farm9.staticflickr.com/8250/8...3d83813a4d.jpg
Both are cut back to cylinder bore, so birdshot patterns are iffy past 15-18 yards, but they work on red squirrels pestering the house!