The 11-87 has a stainless steel magazine tube rather than blue steel.
The extractor is beefier than the 1100 extractor. It also has a pressure
compensating gas system which is supposed to function with 3" or
target loads.The target versions are not pressure compensated. Also
the piston and piston seal are heat treated. Checkering is cut not pressed.
Couple of pics. You can see the extra piece that goes on the end of the barrel lug for the 1187, the forearm must have room for this. That is why you can interchange the butt stock but not the forearm between the two. The mag tube cap is also different. The 1100 has a bearing in the end of the forearm to ratchet on the end of the mag cap. ( 1100 on left, 1187 on right)The 1187 mag cap ratchets off the plastic spring retainer inside the tube. Problem with the 1187 is you have to modify the tube to put a mag tube extension on it. Regards, Bob
1. Barrels are different Field barrels pressure compensating, Target barrels are not they also have Gas Cylinder Collar
2. Comes with different Piston and Piston Seal Interchangeable to 1100 I have not changed to mine yet
3. Extractor is wider .30 inch
4. Magazine tube is Stainless Steel and Magazine spring retainer is different.
5. Forearm is different
6. Magazine spring different number of turns Interchangeable to 1100
7.Fore end Support larger Interchangeable to 1100
8. Action Spring Follower Interchangeable to 1100
9. Firing pin spring coil rate different Interchangeable to 1100
10. Breech Bolt has wider cut for the larger extractor.
I started with a 1100 3inch Mag. 30inch Full Choke for 44 years. It took me 5 year shooting them both to finally come to the conclusion the 11-87 was better with all the improvements.
I have put the Action Spring Follower in my 1100 as well as the Magazine Spring just replaced old one with updated 11-87 style.
While my 1100 is 44 years old and still going strong and items I have had to have fixed Magazine tube my fault from over tightend, Magazine Cap, Piston, Link, Firing Pin, Extractor, Bolt oversized, Breech Bolt Buffer, Barrels seal about one every 5 years, Feed Latch, Recoil Pad on my 3rd, Forearm dropped a boat anchor on it duck hunting. I have 5 extra barrels one Trap, one Skeet, one Imp Choke, one 3 inch Mag 28inch Choke tubes, Slug Barrel. I have repaired everything but the Magazine tube and Recoil Pads.
I have complete faith in it and Hunt Waterfowl with it these days.
Now My 11-87 is 31 years old I shoot Trap with it. Parts broken Zero, I have changed Action Springs when shorter than 14 1/2 inch, One Recoil Pad, One Magazine Spring, One Magazine Spring Retainer, and Barrel Seal when needed. Why has this done so well I learned how to maintain it from my experience with the 1100.
It is my understanding the 1100 Classic Trap has most of the 11-87 improvements except the Stainless Steel Magazine Tube.