A good 12 with a rifled barrel van easily shoot accuratly at 100 yards. I have seen groups as small as 1 1/2" out of my Ithaca Deerslayer II. Some have said they have reliably killed deer out to 200 yards, which I don't doubt, but the trajectory is getting pretty arched. You can never tell how well any gun will shoot so to have someone tell you that a certain brand will shoot tiny groups is somewhat misleading. His particular gun might, your may not. I have also found, just like rifles,, each gun has its prefferences for ammo. You will need to test several brands to see which your gun likes. I prefer a 12 for deer hunting, but I have used a 20 on many occasions and they will work fine, just not as well as the 12 in most cases.