Has the barrel been cut, and re beaded? The shorter the barrel the higher the front sight has to be. If it has been re Beaded with only a bead, it will shoot high That is why the rem 18 1/2 factory barrels were on the pedestal. The really short barrels (8 1/2") sold by canammo were notorious for being like 3 ft. high at 25 yds. Dlask short barrels always had a tall front blade sight. To be honest, most people don't do so good with slugs and bead sights, so it could be a combination of all these things. If you are using slugs on a regular basis, you may want a proper slug barrel with irons. If you want to check, put the shotgun upside down on a table. With the top of the receiver touching the table, the front bead should also be touching, or very near so. If it isn't, that means when you are sighting, you are raising the front bead to the same plane as the receiver and shoot high