I'm not familiar with your exact gun, but many smoothbore slug guns with rifled sights are easily capable of taking deer at 75-100 yds. Try a few brands of rifled slugs or hybrid slugs like some of the Brennekes or Remington Buckhammers to find the best one for your gun.

If you get good groups at 50-75 yds with open sights, and your gun allows a scope to be mounted to the barrel, it may be worthwhile to add a scope.