Hey Tank...
My last S.O. qual was with a 14 inch barreled cylinder bore Remington 870 "entry gun".
We shot B27's out to 40 yards with 00buck and with slugs went to 80 yards with "pepper poppers", which are steel targets that fall when you hit them.
Those targets are 9"diameters. I had no problem hitting them, using just the bead on the shotgun.
If you read the directions on the boxes of most slugs, you'll note that they reccomend a"full" choke for the best accuracy. Having tested many chokes in my various shotguns, the full choke always comes up with the tightest groups.
Something to consider though...not always is full choke the best for buckshot. Some guns prefer a modified or an improved modified for the best patterns. In a case like that, I would go with the modified choke as a compromise for both.
What sort of effective range can I expect with rifled slugs out of an 18" cylinder barrel?
That depends on the size of your target. :silly:
You should have no problem on a man sized target out to 100 yards.The thing about shotguns is you have a rather coarse sight when using a bead, unless you have rifle sights or a scope. I would say that you are more limited with the sighting arrangement than you are with the shot itself. FWIW...most slugs will shoot approx. 10 " LOW at 100 yards.