i have a rem 1100 2.75.

i use a full choke with 000 buckshot ans brenneke slugs through it. ( i know they say not to do it but i have never had a problem with that setup ).people say to try differant lead slugs. but i have found shooting lead slugs in any smooth bore you will not get decent sub M.O.A groups like you would with a rifle or rifled barrle with a scope.
i also have a 21" rifled barrel and have used regular lead slugs and rem copper solids with iron sights. ( i think to optimize the rifled barrel you have to use a scope )