If its adjustable why cant you move it ? If you hitting low , the rear sight needs to be moved back towards the stock. With my H&R , I'm 3" high at 50yds and dead on at 100. Check the ballistics of the slugs , most "juiced" slugs are high at 50yds and level off around 100. Buy a slug with a slower FPS if you plan on shooting less than 75 yds.