Some people don't know the difference between a sabot slug and a foster slug. I'm not saying you don't, but if you don't, and if you have a smoothbore shotgun, avoid buying anything with the word "Sabot" on it. Sabot slugs are made for rifled barrels, which you don't have. They may not be dangerous to shoot in a smoothbore, but they are very expensive compared to a Foster type rifled slug, and most reports say they don't perform any better than a rifled slug does in a smoothbore.
I suggest that you just go out to your favorite ammo supplier and ask for a box of Remington "Sluggers" in your gauge.
Remington "Sluggers" are "rifled" slugs, thy've been around for a long time, and are made for shooting in smoothbore shotguns. The rifling on the slug itself supposedly imparts a spin to compensate for the lack of rifling in the barrel. (I don't know if they really spin or not; I've heard they don't.)
Remington "Sluggers" can be used in smoothbore shotguns with cylinder barrels and in smoothbore shotguns with improved cylinder barrels; but I don't know whether you should use them in guns with tighter chokes than that or not. Maybe somebody else can comment on that.
In my 12 guage smoothbore gun with a 26" improved cylinder barrel, I find that the 2 3/4 inch Remington "Sluggers" are accurate out to about 50 yards. I've never fired a slug in anything but a 12 gauge gun though, and I use 2 3/4 inch slugs only, so I cannot speak for their performance in any other configuration.
I don't claim that Remington Sluggers are any better than the other rifled slugs, but they do have the advantage of being tried and true, they are readily availiable, they hit hard, and they are very reliable and consistent. Works for me.