My 1100 didn't say mag on it if I recall, it came with 2 barrels one 2 3/4" and a 3" chambered barrel. The 3" barrel would not reliably eject 2 3/4" shells as it only had one gas port. The 2 3/4" barrel had two gas ports. That is why the 11-87 came to be. The gas system was redesigned to reliably eject mixed sized shells.