Suddenthunder,
My two sons shot steel through 3" 20gauge Ithaca/SKBs hunting both geese and ducks from age 9 to 14 and never felt undergunned. Both their 20s patterned steel very well, and they routinely killed anything that flew past them within range. You have to pattern a 20 just like you have to pattern a 12 to know what you have to work with. And yes, a Model 311 will handle steel shot.
NCTarheel