On my slug gun I am currently using a Bushnell elite 3200 3-9X40. Works very well for me. My wife also uses the same scope on her 1100. Any good quality scope will work well.Some of the cheaper ones will break under recoil. But, the real problem is mounts.You will have to use a saddle mount that attaches with the trigger group pins. I'm not sure if the 1100 can be drilled and tapped for scope bases. You could also have him buy a new barrel what has the cantilever mount on it, this is what mi wifes gun has. Hood luck.