I found a guy that might let me hunt on his land, but he only wants me to use a shotgun. What is the range of a smooth bore barrel shooting 3" Magnum Rifled slugs? About 75yds? I have a 4x scope on it. And what size groups should I expect?

Guns cause crime, like flies cause garbage.

You shouldn't have any problem at all getting a good group at 75 yards, especially with a scope. My only suggestion would be to give another thought on those 3" mag slugs. About the only thing they are good for is putting some extra abuse on your shoulder.

--Man who fish in other man's well often catch crabs--

I have an old Ithaca Deerslayer with 26" barrel that will shoot into 3" at 100 yards with Remington Foster-type slugs, (old Weaver K2.5). I consider it adequate for deer hunting to 100 yards. But, I don't LIKE slugs-prefer a muzzleloader, where such restrictions apply!

Keep yore powder dry!!

one thing a rifleman must relize is your not going to get those 1/4 inch groups at 100 yards with a smooth bore shotgun.but then again you don't need 1/4 inch groups to get the job done.if you take a 9 inch pie plate(about the same size as a deers kill zone)and from a good bench rest put 5 slugs on that pie plate at 100 yards,your ready to go.100 yards or a touch more will or should be your max range with a smooth bore.its important that you try as many different brand slugs as you can find or afford.you will be amazed at how differently each manufactorers slug will shoot from your gun.im going to agree with indyhunter about the 3 inch slugs but if thats what shoots concistanly out of your smooth bore then by all means shoot them.to start out try the 2 3/4 inch slugs in 1 oz and 1 1/4 oz wieghts all the companys make them,remington-winchester-federal-active-brennekee and so on.try them all if you can.realisticly speaking,any where from two to five inch groups are the norm.group size is a direct result of the amount of testing you do.so again,shoot them all if you can.

While I agree that a smoothbore with rifled slugs and a scope can be a 100 yd. gun from a rest I would take that same paper plate and do some more realistic hunting situations and see at what range you can consistantly put your shot on the plate.

my buddy that hunts with me in my home state uses a marlin model 512 bolt action slug gun. he has a trashco fixed 2.5 and uses brenneke gold slugs. he gets decent groups out to 100yds.
i used a smooth bore rifle with a scope on my former 870 wingmaster and i only got decent groups out to 75yds. not bad range especially since in my state they don't get longer than 50yds.