get out a good gun best if incendary or even better if corrosive and go insane and bullet spray everywhere.
Or... you can use some strategy. Sledge will stop shooting if you get close enough, and use his hammer attack instead. You can fire at him while he's winding up, then be ready to take a step into complete cover while he slams down. Using a corner in the hallway is very effectvie for this. Also, if you can manage to get behind him, the back of his head is a critical spot. Continuous damage from elemental attacks is very effective, and will keep his powerful shield from regenerating.