Re steel shot. Mostly I'm leery that lead shot might be outlawed. Am also a little worried about filling fields where we grow most of our food with lead. But also, there are grass seed fields near home that flood and have hundreds of geese on them in winter, and I'll bet owners would be overjoyed with anyone who wanted to shoot the geese. The geese cause a huge amount of damage.Just spitballing here:
@OldBroad44 Is there any reason you mentioned steel shot? Do you live next to water? Or is it a general environmental concern?
With lead shot, a full choke would be my choice for nuisance birds. I'm thinking they will be farther away and maybe even not flying at the time of the shot. Maybe sitting on the stalks? In that case, you're going to be aiming the shotgun more like a rifle and have less to learn than hunting that requires the shotgun to swing. Less swing allows you to use a tighter pattern, increasing the capability to shoot farther away.
I still like slug barrels for hunting deer with slugs or buck vs using a standard 28" barrel. The shorter barrel is easier to pack thru the woods, and you usually have a "set" of sights, front and rear like on a rifle, compared to the bead at the end of your standard 28" barrel.
As for the birds in the corn--
I'm a plant breeder. (Geneticist by training. Freelance plant breeder and author by practice.) Mostly corn, beans, and squash. I work in collaboration with local farmers. The farm collaborator is responsible for keeping birds out of the corn. But my main local collaborator certainly wouldn't mind some help. And I'm often over there anyway doing crosses, evaluating stuff, etc. So there's not strictly a need for me to go after the birds in the corn. But there's enough of an excuse, I deem, to justify getting interested in a new (to me) kind of gun. And also, there's that spot close to home that is full of deer but is shotgun only.
The birds are blackbirds. If not at least harassed regularly daily from the milk stage of the corn to harvest, they'll destroy nearly all of it. The corn tassels are about 6 or 7 feet high. The ears are about 3 to 5 feet high. You can't really see the birds that are down on the ears. And even if you could, blowing away the ears or filling them with lead wouldn't be useful. Occasionally my farmer can kill a "sentry" bird that is up on the tassels. But most of the time he shoots over the corn to scare them off. The flock will usually fly off after two or three shots. He also uses a cannon. It takes the combination of the cannon and harassing the birds with a shotgun pretty regularly to get a corn crop. He uses an old 870 with a fixed choke. The occasional sentry bird that is up in the corn tassels is usually at about 50 yards. Its a shot that's difficult with the choke he has, but not impossible. I think you are right that for these shots a full choke would work better, and you're actually using the shotgun more like a rifle.
Crows sometimes go after newly seeded corn as it germinates and pull up the plants by the shoots to get the kernels. They can get nearly every kernel, necessitating replanting. They are usually shot with a shotgun. If you leave the first couple of dead crows in the field, the entire flock will usually abandon that field. Not so with blackbirds.