Fraze,

You can use rifled slugs in your smooth bore, as for distance I don't know what to expect, as I have always used rifled barrels, My personal limit is around 125 yards... You should be able to find saboted rounds for your gun as well.

If you ever go get another gun I suggest an H&R breakopen 20 gauge with a rifled barrel, mine has been superbly accurate for a slug gun and it is very inexpensive, I have the heavy barrel so the gun weighs like 10 pounds though.