The 11-87 has a stamped metal adapter that goes over the end of the barrel gas ring to allow cycling of 2-3/4" loads. It acts like a cap to retain some of the escaping gas so the action can cycle the lighter loads. You should always remove this ring when firing hot 2-3/4" or 3" magnum loads. Otherwise, it will cycle the bolt way to fast. This can cause timing problems where the next round is dumped on the ground. It also slaps the heck out of the gun and shooter. So, the differences between the 1100 & 11-87 are primarily in the barrels. The Remington site specifically tells you not to interchange the barrels between these models, so I won't tell you that my 11-87 barrel works just fine on my 1100 Magnum.