Am new to the list, and new to my 6920.
I am a minimalist who would like to mount a Surefire-type light to the carbine. I would like to, for the moment at least, stay away from rails and such.
Is there a good mount that will attach to the weapon as is? Preferred method would be something directly above or below the barrel - not off to the side.
TIA
john
I’m looking at something like this for my 16" Rock River… I don’t want to go with rails on this gun.
ETA: The image is from Cheaper than dirt… linky, but I’d like to get something of better quality.
You can use a TDI arms polymer rail segment. It bolts directly to your stock hand guards on the top or bottom.
With that as your base, you can use a TDI mount and put a G2 flashlight onto the rail for a cheap and easy quick attach light system. Or just slide an M3 light onto the TDI rail… Not permanent alterations to your gun and no messy rail systems! 
Try the Elzetta flashlight mount that attaches to the front sight base. It is inexpensive, works great, and does not require rails.
Get details at www.elzetta.com
I posted an earlier thread at http://m4carbine.net/showthread.php?t=7717
As you will read, some people think that it is ugly (I don’t), but there is no denying that it works great. I especially like the sling swivel activation of the pushbutton switch on the Surefire G2.
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Actually, I think most people just object to the fact that it’s plastic.
A company makes a plastic mount that affixes to a FSB? That seems like a great idea.
Although I’ve only shot with it once so far, it took three consecutive 30 round mag dumps on full-auto (borrowed my buddy’s Class 3 lower). The barrel was steaming but the plastic Elzetta mount held tight.
(With the price of .223 ammo, that was the most abusive test my budget could afford.)
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Here are some pics of a Surefire M16 mount and weaver ring I have on one of my uppers. Traditionally, the light is mounted at 6:00 with this mount. I have rotated the light to 11:00 so I can activate the light with my support hand thumb. One could position the light anywhere between 1 and 11 o’clock depending on user preference. The mount is rock solid. I like it better than the FSB mounts because the light sits closer to the bore line on the horizontal axis.
Here’s a couple of options from Sage Int’l.
http://sageinternationalltd.com/si/access/m16.html#lightmounts
I have no experience with these, just happened to see them while looking for another Sage Int’l accessory.
Wow, I wonder what kind of polymer it was to take the kind of heat that a gasblock would create after 90 rounds of full auto?
The Elzetta FAQ page (http://www.elzetta.com/Webpages/faq.htm) says that it is made from “glass-filled nylon” (like many accessories) but judging by the swirly surface finish, I’d say that it has a higher fiberglass content than normal.
Also, there are little ribs on the inside of the two halves that contact the gas block and the barrel. These probably help to minimize the heat transfer to the plastic.
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I put on one of these on my 6920 and it is aluminum and has held tight so far. Less than $35.
M_P
Lights on the bottom are a problem while trying to use any type of rest I.e., barricade, window, sand bags, Gear Bag, etc.
IMHO…best to place it on the FSB at the 3:00 or 9:00 position. 12:00 obviously won’t work.
Tack
Good point but the problem with side-mount setups is that you have to remove them to store your rifle in its case (unless you have a custom case). For me that’s too much hassle and I want my rifle to be ready for action at a moment’s notice. The bad guys won’t wait for you to assemble your gear.
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I didn’t get that memo.
Bob
Me neither. 
Says WHO???
OK, evidently some of you either have very slim side mounts or your rifle cases are much thicker than mine. I use the cheap plastic case that my DPMS came with and it is just thick enough to hold the rifle in its stock configuration. None of the side-mounted flashlight holders that I have seen would work with MY case. Sorry for the over-generalization.
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Ummm… never mind.
goes to bed