KAS RAS won't clear Delta Ring on 6933

[OH58D]

I am almost embarrassed to post this, since I have installed several Knights Rail Adapter Systems on both Colts and LMT carbines. Tonight I have been attempting to install as new RAS on my 6933 and I cannot get the top rail half to clear the delta ring. I have even used two different delta ring tools but the ring bottoms out without allowing the back end of the rail to slide on. This has never happened before and I am at a loss to figure this out. I've tried it horizontally to allow the rear RAS clamps to slide over the gas tube, but the delta ring does not retract far enough to seat the back end of the rail. I will add that the teeth of the barrel nut seem to be catching on the inside of the top rail at the back end and are gouging in the inside of the rail.

Any suggestions?

[wildcard600]

Possible dumb question, but did you remove the tension screw ?

[OH58D]

Possible dumb question, but did you remove the tension screw ?

Oh yes, first thing I did. I have installed these things dozens of times, but never a problem like this. I took off the RAS on one of my other carbines and tried to install it on this new 6933... no luck. It's almost like the barrel nut protrudes out further on this Colt, even though it is tight. The teeth of the barrel nut are gouging the rear sides of the RAS upper.

I took a file and found where the barrel nut teeth are gouging the rail and I filed it down, then sand papered it a bit. Still wouldn't go on. Now I am trying something different. I have installed the lower have of the RAS first, holding it in place horizontally and installing the upper half, allowing the clamp to drop down on each side of the gas tube. I can just barely get the upper half on but it does go on, but VERY tight. I'll get some Birchwood Casey Aluma Black tomorrow and cover the white aluminum inside the upper half of the RAS and reinstall.

I am thinking this 6933 may have a barrel nut which protrudes too far and interferes with the top rail dropping down properly. Has anyone seen this before? As I said before, I have installed dozens of these KAC RAS rails for the carbine and have never experienced this before.

[wildcard600]

does the barrel nut obviously protrude out farther than one of your other rifles ? Maybe the issue is at the other end with the handguard cap ? Strange either way.

[bigwagon]

Are you sure the front end of the rail section is fully seated in the handguard cap?

[OH58D]

Thanks for the responses. Keep in mind I've installed these on five other weapons, including a 10.5 LMT SBR and a Colt M4 SBR with 14.5 barrel, in addition to other 16 inch barrel Colt 6920s. Normally very simple. Slide the front end of the top rail all the way under the front cap, pull back the delta ring and push the back end down, making sure the clamp drops in on each side of the gas tube. The lower installs just as easy or even easier.

I can say that this delta ring on the 6933 is stiffer than some I have run into, but I am using the delta ring tool to press it back. It just seems like I run out of room with the delta fully depressed and it won't let the back end of the RAS clear it. The teeth from the barrel nut then gouge the inside of the RAS on each side.

My first thoughts are the delta ring bottoms out earlier than other AR carbines I own. If I have time today, I may measure the distance from the front end of the delta ring to the back end of the front hand guard cap. Maybe the distance is less on this 6933 with the 11.5 barrel?