I'm assumming you mean 11-87. The 1100 is 2 3/4" chamber. The 11-87 is 3" chamber. If I am not mistaken, that is the difference. I bought my wife an 1100 slug gun this year. She loves it. This is the one she has.
http://www.remington.com/firearms/shotguns/1100FRCL.HTM