Good evening to you!! The Mossberg 500xlb 12 gauge 24" SB RB ported has a 3" chamber which will support both 2 3/4" and 3" slugs with no issues. Hope this was helpful. Have a good rest of your weekend.

Yes, both 3" & 2-3/4" shells can be loaded in & fired.

Hi Lonnie and welcome. Yes Sir, this 24" Rifled Barrel with Cantilever Scope Mount has a 3" chamber and will fire both 3" and 2 3/4" Slugs no issue. Cheers, stay safe and enjoy!

Hi Lonnie, yes this is compatible with bot 2 3/4" and 3" shells.
Stay safe & have a great day!