Regarding choice of ammo:
NO BIRDSHOT. I repeat; NO BIRDSHOT. Birdshot is for birds, buckshot is for Bad Guys. Buckshot pellets, being more massive than birdshot, conserve their kinetic energy better and therefore penetrate deeper and inflict greater shock damage.
The Box O' Truth #3 - The Shotgun Meets the Box O' Truth - Page 2
The Box O' Truth #17 - I Hear You Knocking - Metal Doors - Page 1
The Box O' Truth #14 - Rifles, Shotguns, and Walls - Page 4
NO BIRDSHOT.