Here is my review on a light mount that can be used for the Mossberg 930:



The Streamlight 69906 mount is listed for the Remington 870, but I took a chance since I have owned both and they were of similar dimensions where needed.

http://www.opticsplanet.net/streamlight-rem-870-tactical-mount-69906.html

The mount has rounded cutouts for the barrel, to prevent rotation of the mount, and even though the 870 and 930 are different animals, the mount drops right on without a fuss.  It can be mounted at the 3/6/9 o'clock postions.  The mount ring also has a recessed area that the base of the mag cap/mag tube fits right into.  The smooth, metal area actually helps because in the case of the Choate mag extension, there are small teeth that dig into the plastic forend which can make for a difficult time trying to remove it later.



Due to my search for a mount like this, a common issue arises in that the L-shaped mount could be bent if smacked or dropped, but after installing it in the 6 o'clock postion, the 930 forend meets the back of the rail and provides plenty of support.  The 3/9 o'clock postions do not off such support, nor does any of the rail-forward postions.  Of course, the steel on this mount is just as tough as the mag extension, so any impact hard enough to really screw up the mount would most likely crater the flashlight being used.



I will eventually have a detachable light like an XML or TLR1, but the Pelican M6-LED and ring are shown for size comparisons.  Unfortunately, the ring shown is not a 1" ring...I need to hunt one down.  But the mounting shows easy access to the clickable switch on the back of the M6.

Interesting...thanks for the review/pics.

The only issue that I can see that may be troublesome is for folks like me who are running a Scattergun Tech. sling plate that installs in the same spot and puts the sling loop coming out right where the forward edge of the rail is.  I suppose you could turn the rail mount so that it becomes a 3 o'clock position mount instead of a 6 o'clock position mount, but then I worry about having the width of two mounting plates (the sling adapter and the rail adapter) in that same spot and weakening the setup of the mag extension.

Thanks again...

I don't believe in using slings on home defense shotguns, but I see your point.  If I really need to add a sling for a short duration, I do have the barrel/mag clamp that came with the Choate extension.  It allows for a sling on either side.

Another issue that may be even greater is the gap left between the body of the extension and the actual mag tube.  If there is enough of a gap there, the follower can bind.  That will leave you with no spring tension on the rounds between the gap and the loading port.
Slings are usually a good idea, even moreso on HD shotguns.