I had put on a 10 round extension on my Rem 11-87 (26") from Tac-Star. An okay tube except for a few things.
1 : It's blue. The shotgun is matte black. (This can be corrected with a little paint.)
2 : There should ba a spacer for the sling swivel stud to make it stick out farther from the barrel clamps. As it is my QD sling attachment has limited movement due to interference with the clamp.
3 : You have to use the stock mag follower.
They do make a 7, 8, and 9 round extension. The 9 rounder should fit your 1100 (23) okay.
Got it at : http://www.ajaxgrips.com/
Choate also makes mag extensions in 7, 8, 9, and 10 rounds and also has a parkerized option for the 9, and 10. They also come with a high visability extended follower, I think. The extension on the follower is suppose to keep the mag spring from kinking, which I think the Tac-Star is doing in my gun as i can only load 9 rounds comfortably into it. Not sure how well their swivel stud works on the clamp.
They can be bought at :
In any case, if you have bought a newer 11-87 (no sure if this also goes for the 1100), you will have to grind down the magazine cap retaining dimples inside the edge of the mag well. You'l have to grind them down pretty close to flush as the follower would bind on it if you don't.
- Ron V.