Smoothbore slug gun with rifled barrel extension
So I have recently had a browning bps 12 ga. Slug gun handed down to me by my father who had won the shotgun in a raffle well over a decade ago, the gun is a smoothbore shotgun with about a 20 inch barrel length and fixed iron sights, however it has a 3 inch rifled extension at the muzzle, does anybody know about these extensions? Did they come standard? Does that last 3 inches of rifling really make a difference? And should I use rifled slugs or sabots when I am deer hunting?
If anybody has some advice for me I would greatly appreciate it
Thank you