BudsGunShop.com - Steel shot

John, from Mossberg -- Barrels with an interchangeable Accu-Choke™ or Accu-Mag™ choke tube system, yes (with proper tubes installed.) However, steel shot is not recommended for older “C-Lect Choke®” or fixed-choke barrels. --- >>>> mossberg.com/can-i-shoot-steel-shot-through-all-barrels/

from what I understand an (read from the provided link " both barrels are fine with steel I understood it as OLDER barrels either select choke or fixed choke should not use steel but Newer barrels both accu-choke and fixed are fine. however you should not use steel through a full choke barrel I would contact Mossberg and ask to be sure Tel: (203) 230-5300 | 8:00am-4:30pm Eastern

John, the 28 inch barrel is Steel Shot rated and the 18.5 inch Cylinder Bore (Defensive Barrel) is not. Cheers and stay safe!