ORIGINAL: Hurricanespg
For the duck hunting just get you one of their 26"-28" barrels with interchangeable chokes. For slugs look at the rifle/cantilever barrel as mentioned above, but I would recommend shooting the 2-3/4" shells. They are generally more accurate than the 3".
You should never use 2-3/4" shells when using slugs in a shotgun that is chambered for shells up to 3.5". Here is the information I got from the LIGHTFIELD SLUG WEB PAGE:
Q:
Why can't I shoot 2-3/4" slugs through my 3-1/2" chambered slug gun?
A:
Firing a 2-3/4" slug in a 3-1/2" chamber is not recommended because of the length of the jump the slug makes between the end of a 2-3/4" case and the front end of a 3-1/2" chamber. This can cause misalignment of the sabot on the slug, thus causing a serious pressure problem as well as poor accuracy. Slugs are NOT LIKE SHOT SHELLS where a shorter shell can be safely fired in a longer chamber with no ill effects. The bottom line is you should use a shell with a minimum case length of 3" (ideally 3-1/2") in any 3-1/2" chambered rifled barrel for best accuracy. THE CASE LENGTH SHOULD MATCH THE CHAMBER LENGTH WHEN IT COMES TO SLUGS.