RE: Shotgun Deer Hunting Question
I have a Remington 870 12GA. It's plenty powerful for deer. I'm not sure about your 20GA though. I might be good, but then, the 12GA would be the best bet out of the two.
I also have a smooth bore 28" barrel on my 870. I use these choke tubes:
#00 Buckshot: Full choke (maybe Modified depending on conditions).
Slugs: Improved Cylinder. (you have to use IC with slugs and you have to use Rifled slugs - i.e. Remington Sluggers).
Butch