Back in the "BS" days (Before Steel... ) your barrel would have been a Duck/Goose barrel. Today, it's a Turkey barrel and not much else. Steel won't pattern well in it although, as you mentioned the smaller shot sizes will probably pattern better than the larger. Steel shot typically patterns one choke tighter than lead UNTILL you get to full choke and then the pattern starts to open. If you plan on going duck and goose hunting I'd just open the "full" choke on your barrel up a bit to modified or have a gunsmith do it for you. Then you would essentially have a full choke gun with steel for waterfowl and a modified choke gun with lead for whatever else. You might shoot a load of steel through it first at a pattern board to make sure that it hasn't already been opened and to see what kind of patterns it throws ”as is.” Sometimes, even with lead shot, a barrel won't pattern or be choked exactly as marked with whatever shells you use. You can probably open the choke up yourself with a few "shade tree" techniques. First off, on most full choke, 12 ga shotguns (though not all, but on a Mossberg this should work) a dime will NOT pass through a full choke, but it will through a modified choke. Check yours and then with either a brake cylinder hone (this works the best, remember to oil the hone) or a piece of fine Emory cloth taped and then wrapped around a doll rod, chucked in a drill, run this lightly back and forth in the last 2 inches of your barrel. Stop frequently to see if your dime will just pass through and don’t get too carried away. When a dime will just pass through STOP and pattern your gun again. It should shoot a tighter pattern with steel than it did before.