30-30 medicine gun

[Jack]

YukonGirl, welcome to HuntChat.
A Mossberg smoothbore barrel will come with 3 choke tubes- Improved Cylinder, Modified, and Full. Those 3 will cover most things you'd want to do with shotshells.
As far as firing slugs, there are a few ways to go. The rifled barrels will fire sabot slugs quite accurately. However, the rifled barrel is a specialty item- it's really good only for slugs.
Another option is to shoot slugs out of the smoothbore barrel. Not as accurate as the rifled barrels, but you can use one smoothbore barrel for shot, slugs, and buckshot, too- more versatile.
Usually the Improved Cylinder choke tube will work best with slugs in a smoothbore. Use the Foster type, traditional slugs- they usually do as well or better than sabots in smoothbore barrels.
A third option is a rifled choke tube. Generally you have to buy that separately. Not as good as a rifled barrel, in terms of accuracy, but usually better than a smoothbore- kind of a compromise.
That should be enough to be confusing!