Yep, when you change barrels you're best off sighting in again. Iron sights are OK as nyantler attests. Mossberg lists two slug barrels for the 535, both rifled, one iron sights one cantilever scope mount. The deciding factor is how far do you want your effective range to be??? Less than 50y, stick with your bird barrel and bead. Not sure if a 500 smoothbore barrel with iron sights will fit your 535 but if it does, you might find one used. Still good to 50+y but you've upgraded your sights. Either of the rifled barrels and some sabot slugs will pound them at 100y. Your choice of barrels depending on your wallet. Shoot straight!