What is the difference between a Remington 1100 and a Remington 11-87 Shotgun?

The main difference between a model 1100 and an 1187 is, the 1100 is a semi-automatic auto loading shotgun, and the 1187 is a pump shotgun.

Sorry, but that doesn't appear to be correct-the 1100 and 1187 are both autoloading shotguns-the Remington Pump guns are the 870 and the 887. The 105 is also a new autoloading gun. I still can't see any difference between the 1100 and the 11 87.....

The 11-87 "replaced" the 1100 for a short time. The main difference is the gas system which handled light loads and magnums without any adjustment. If you wanted a magnum in the 1100, it had a single gas port and did not handle light loads with that barrel. the 11-87 did a better job of that function than the 1100. However, the 1100 was so popular that Remington had to reintroduce it, especially among clay target shooters. Hope this helps.