Will it shoot slugs and buckshot...

Safely? Sure. Some people claim that shooting rifled slugs through a full choke will damage the gun, but I don't think that's true, at least for the Foster style slugs. My dad has shot hundreds, maybe well over a thousand, Rem Sluggers through his fixed full choke 870 Wingmaster 20 gauge over the years and it still patterns fine and there is nothing wrong with the barrel. It always gave acceptable accuracy, too. Buckshot is also safe to shoot, but whether is patterns worth a darn is an open question. You'll have to pattern it to find out for sure, and it may like certain brands/configurations of buckshot better than others, so you may want to try a variety of different shells.

Good luck,

Mike