I got a KAC drop in quad rail for my stock Colt LE6920 and can't get it to install correctly. There seems to be an assembly in the front that is supposed to hook under the barrel nut and tighten down with a screw to keep the rail level with the upper rail but I can't get the barrel nut depressed enough with the standard installation tool that hooks into the mag well to allow this part to get under the nut, even if I loosen the screw holding it all the way. If I remove the part it goes in just fine but the back of the rail stays a tad elevated above the upper rail and is not level. What am I missing here? It seems to be necessary to insert the front of the rail into the front ring on the stock sight/gas block first. The Colt is stock configuration.

Hope that helps; I have both rails and I am installing one on my M4 upper (Colt M4 14.5 barrel, Y/M Bolt assy., BCM upper, Matech BUIS, TA31 RCO-M4P, Surefire M952). It's a bit tricky to slide the clamp around the gas tube and under the barrel nut, but it can be done.

Youre sliding the front side of the rail into the handguard cap first, while keeping metal tab on top of handguard cap correct? At this point you should be able to depress the delta ring by hand and snap in both sides of rear half of the rail by squeezing them together (with screw loosened and d-ring fully depressed) ETA- are you installing the RIS or RAS? My description was for the RIS but the RAS is a slight bit different installation

Perfect. Thank you very much. For whatever reason mine did not come with this instruction sheet. My next step was to try the installation with the screw removed. I'm going to go down and install it right now.

You're using some incorrect nomenclature here and there, but basically:

Angle the rifle at approximately 45 degrees, muzzle pointing up.

Loosen or remove (depending on whether you have a captured screw or not) the screw that secures the barrel nut clamp until the "claw" hangs free from gravity.  

Insert the front end of the RAS into the front handguard retaining cap behind the FSB, making sure that the silver leaf spring goes under the handguard retaining cap, and maintaining pressure on the leaf spring while pulling back on the delta ring, ease the handguard back to the barrel nut.  

Ensuring that the clamp goes around the gas tube, and with the rifle still angled, maintain rearward pressure on the delta ring, and give the top of the rail a good smack, and it should seat into place with the claw under the barrel nut, the barrel nut notches aligned, and with the top rail level with the upper receiver.  

You may have to try it a couple of times before you're able to get it right.

I'm sure there are more than a couple YouTube videos on the KAC M4 RAS install as well, though I haven't looked them up.  

ETA: Damn, y'all are quick.  

~Augee

I see where I referred to depressing the barrel nut... oops. I knew better than that. Thanks for the correction. I went right down and backed the screw out completely and the rail went right in as it should; Had my rail come with the directions I would have had it the first attempt. I will say that you have to tighten the screw a bit more than finger tight to bring the back of the rail down to nearly lining up level with the upper rail. If you just barely snug it the rail slopes forward a fair bit. Not sure if that makes any real difference.  I just watched the attached video; he sure went over "finger tight" on his clamp screw.

Don't remove screw as it states in directions that came with mine.

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