Does it have a PolyChoke or the like, or just a plain fixed choke?
What gauge?
If it's in good shape, with a fixed choke barrel, it should handle slugs OK.
I've had good results from Brenneke KO slugs in every smoothbore I've tried them in so far, and recommend them highly. They aren't overly expensive, either. But KOs are only available in 12 and 20 gauge as far as I know.