Shotguns vary widely as to what any accessory will do. Especially, choke tubes.
I have two 870s set up to use slugs as needed. One is chokeless, just cylinder bore. The other, during the season, wears a rifled choke tube.
With the best slug from a solid bench and good technique, the difference is about 1 inch.
YMMV, and probably will.
A buddy's Express,with that very same tube in it, sprayed one brand of slug over the paper at 50 yards. We both shot it and found it so with his slug of choice. Replacing the tube with an IC saw great improvement, and changing the slug to a rifled slug even more.
8" groups went to sub 3".
And then I tried the tube in MY barrel with HIS slugs and got decent groups.
Go figure.....
In your shoes, I'd get a rifled choke tube and lots of different slugs. Sabots are best in fully rifled barrels for the most part. I'd try old style rifled slugs and the various Brenekkes.
HTH....
