Is it a fully rifled barrel or smooth bore? If it is rifled I would take a look at the Remington Copper Solids, or some of the other sabot slugs...they are pricey but most high end slugs are. If you are shooting a smooth bore you can stick with plain old foster-style slugs. This past year I sighted in my 870 with the cheap winchesters and it shot big ragged holes at 50 yards and kept pie plate accuracy out to 100 yards. From what you described this should be plenty accurate, and much less expensive then shooting sabot style slugs designed for rifled barrels. Hope that helped a little and good luck!