RE: 11-87 Barrel
If I'm understanding this correctly,the 11-87 supermag is a 3 1/2" shotgun and the barrel you're asking about is 3". The answer is NO it won't fit. You have to match them up-if you've got a 3 1/2" gun,you'll need a 3 1/2" chambered barrel-not that you have to shoot 3 1/2" shells out of it,just so that it will fit in reciever correctly(different length).