I had mentioned ordering one of these in another thread, and had a couple of requests from guys wanting to know my opinions of it, so I decided to make a thread and share my thoughts. Here is a link to the product on Brownells: MAGAZINE EXTENSION SUPPORT CLAMP - Brownells
As it says in the title, I ordered mine with a rail, so that I can mount a light on my shotgun. I currently have it mounted on my Mossy 930 SPX. But it can also be mounted on an 870 with a magazine extension, or on a Mossbery 500 Persuader, although on that it functions only as a way to have a rail, not as a mag extension clamp.
Install is easy, the two halves of the clamp are separate, and held together by two screws, with one coming in from each side. So you put the parts on the shotgun where you want the clamp, and then just screw the two halves together, I added some blue loctite. Then there is a screw hole on each half, so you can mount the rail section on either the right, or left side of the shotgun. There is only one connection point between the rail and the clamp, so I am hoping that is holds up without any issues. The bottom half of the clamp is slightly larger to fit the mag extension tube, so it is flared out just below the rail when it is attached, which should help the rail from moving.
The single attachment point between the rail and clamp, and the fact that the rail section is only an inch long (making it too short for the mounting base on my Surefire WML) are the two things I don't like about it so far. I did get the surefire mounted, and tightened down on the rail section securely, I just would prefer enough rail to fill the whole base, which would take about another half inch of rail space.
I do have a day of busting clays scheduled tomorrow with some friends, so I will be taking the 930 along with me, and put it through it's paces, and see if anything comes loose or has any issues, but I don't forsee that happening. So I will update this sometime this weekend to add my comments about how the new addition holds up under firing, I am hoping to get about 100 rounds through her tomorrow. Yes, I am going to go shoot clays with my 8 shot semi-auto with ghost rings, I've actually done it before, and it usually works surprisingly well.