Used on my 870 tactical fit and finished were awesome. While shooting the clamp slips on the barrel and the extension tube and it ruined my finish I called Mesa tactical and they they sent me thoes rubber things that going between the receiver and the sidesaddle carrier and said to try it by than I gave up no matter how tight I torque the bolts the clamp still slipped

I used this on a Remington 870P 20" Barrel and Tac Ordnance +3 Magazine Extension Tube and It fits too tight causing the barrel and magazine to stretch away from each other ultimately causing a magazine failure to feed shells because they get stuck where the Extension Tube connects to the Shot Tube. I really like this product I just wish it worked, Maybe I got a bad one, I'm contacting Mesa Tactical on this so I can see what my options are. Also I spend 2 days trouble shooting this and I am 100% sure that the issue is with the Mesa Tactical Magazine Clamp and not the Follower as I have tried 3 different followers in the trouble shooting, Plastic, Aluminum, Stainless Steel. I will Edit this review if they Mesa Tactical helps me out here I'm thinking I might have received one labeled as 870 when it could be mossberg, I dunno.

I bought both this clamp/mount as well the Nordic Components product (also avail. at Browmells) in an attempt to find a way to mount both a flashlight and a sling swivel on a standard Mossberg 590. While the Nordic product was advertised to fit the Mossberg 590 specifcally, it did not fit nearly as well as this product which appears to be directed toward the Rem 870.

The Nordic mount fit OK, but there was a considerable amount of barrel and magazine tube radius that were not in contact with the mount. This clamp from Mesa fit really well and had what appeared to be complete contact with the curvature of the barrel and the magazine tube. I am not sure how this would fit a Moss 590 A1 as I beleive the barrel is thicker on the A1 (larger radius ?), but it works quite well on the regular 590.

The four star rating is due to the fact that it seems that the holes in the halves of the mount were drilled and tapped prior to the application of whatever sort of black surface coating was applied. As a result, the first 0.25" of the screw holes were very difficult to screw into. Fortunately, it seems that an extra screw was provided, so I used it as a sacrificial "starter" and thread cleaner to allow for easier assembly.

This accessory is not cheap, but it is very well made and allows the use of standard push-button QR swivels and the option to install a rail for a flashlight or whatever other sort of rail-mounted accessory you want to hang out there. Note: you can install the rail on either side and both sides have sling attachment sockets, but whatever side you put the rail on, you will cover the sling attachment point

Lastly, if it matters and you haven't thought of it yet, you WILL need to remove this mount each time you want to remove the barrel for a thorough breech-end cleaning. This is true of any such barrel/mag tube clamp, so it's no indication of an inferior design with this product.

Installed on my Remington 1100 with a Dave's Metal Works mag tube extension. Clamps perfectly around the mag tube.
There is a tiny gap under the barrel, but the left and right sides are solid and locked against the barrel.
Well designed with a screw on the left and right side of the clamp to even out torque and clamping forces. Take your time and you'll only install this once.(aside from having to take down your 1100/870 for cleaing around the mag tube especially for 1100 owners)
Only gripe is that you get one allen wrench. The one supplied fits the screws to clamp the two pieces together, but does not fit the 4 other screws for mounting a rail or sling point. No big deal, but would have been nice to be included.
Brownell's price was right in line with competitors. In fact, I ordered the same clamp from a smaller supplier. Unfortunately, their stock keeping is terrible and I found out later it was out of stock and back ordered for 3 weeks or more. So I paid an extra $10(Brownell's was $3 more for the part and shipping was free from the smaller supplier, but deal was indeed "too good to be true.")
Brownell's came through for me big time!
Very satisfied and highly recommend this clamp to all shotgun enthusiasts.

The mount is well made and solid. The picatinny rail however is about half the length shown. It still works fine for my scout light, or I would have pushed the issue. If the rail had been as shown, five stars.

Absolutely bulletproof part and very well built.
All threads have Heli-coil inserts... and it fits perfectly on my 870.
I thought it was a tad pricey, but after handling it, it's worth every penny. I wouldn't hesitate to buy another.

Fit Perfect on a Win. 1300 Defender. Put it on mag tube & barrel and I mounted a Streamlight on the rail. I can activate the light with my thumb WITH my hand gripping the forend. That's a good setup.