I just installed a 13.5 urx3.1 handguard using a Bcm mk2 upper and a 16” Bcm elw barrel. Both the upper and barrel were used together previously with a different handguard for about 1000 rounds. Wanted to try out a urx3.1 so I rebuilt the upper using this one. Followed the instructions and videos I’ve watched on it. It’s timed perfectly, but the barrel is not centered in the handguard perfectly. The last handguard was a bootleg piclok, and it was centered prefectly. It’s not off by a huge amount, and is hard to capture on camera, but I’ll do my best to include a picture or two. It’s probably between 1/16 and 1/8”. Picture

Definitely enough to trigger my OCD.  That is a lot of windage for the rear sight to accommodate as well.  I don't know enough about those rails but with some you can adjust that by tightening screws in a different sequence.

Yeah triggers mine as well. The handguard threads directly onto the upper receiver threads, and the barrel nut is on the inside of the handguard, and pushes against directly the barrel extension. It’s a pretty sturdy design, I think someone just isn’t right with one of the components being used. Not too sure

I have installed many and only 1 was a bit off so I did some searching and saved this from that search.

Those are my Instructions I wrote while working for Knights, and in fact my hands and workshop in the photos.
The key to successful "at home" URX installation is use of the Vise Jaw Assembly 22515 which clamps both the upper receiver rail and URX top rail into alignment, but even more important given the damage to his barrel nut, is its ability to resist torque. Torque lines-of-force move equally in both directions as force is applied, so if you are not holding the work piece solidly, you have no idea of how much you are applying as the work piece moves away from the torque line-of-force being applied.
I have read where some use a carrying handle bridging the upper and the top rail, or others who use a magazine well block to secure the work piece…short answer: unsatisfactory for URX installation.
The URX barrel nut damage described above is at least partially the result of too much torque applied while the work piece was moving in whatever holding fixture/arrangement he was using; but also that he was not pushing and holding the wrench firmly into the barrel nut as torque was applied.
I state this because I have removed as many Loctite’d URX nuts as I have installed, and the loosening of the URX barrel nut requires more torque than you would imagine. And if I did not have the 22515 in a stout vise resisting the torque, I would not have been able to successfully disassemble and re-use as many URX barrel nuts as I have.
I also don’t see reference to the medium strength Loctite per the instructions. But at lease if he didn’t use Loctite, the damaged barrel nut will be a bit easier to remove. If it was me, if the nut is as tight as it reads, I’d finish assembly, shoot the weapon and periodically try to rotate the barrel to see if it ever loosens. If it does, the barrel nut will be easy to remove.


Old Steel nut was 75 +/-

New Alum nut is 55 +/-

A)Depending upon how one threads the URX onto the upper and how it "clocks" can affect how it eventually sits on the upper and lines up.
B)Depending on how square the face of the upper is to the barrel extension this can also affect how the barrel sits inline with the receiver.

3) "Corrective actions" are as follows -- lap the upper to ensure it is square both on the face of the upper receiver extention and the face of the upper where the URX clocks - then lap the end of the URX so it clocks 100% onto the upper. I saw that in brackets as that is the one way I have seen that will guarantee that the URX and Upper are aligned 100% in the same plane.

A cheating method is to use a larger vice block and effective force the upper and URX into alignment -- the only issue with this is when fired at a exceedingly high firing rate it is possible for the loctite to loosen and the URX can shift slightly on the threads.
If you don't want to ever remove the URX, you can use Green high heat large gap loctite  

BARREL NUT 50-55 ft/lbs torque.

 40ft/lbs, backed off, back to 40ft/lbs, backed off again, and then to 55ft/lbs.

Torquing it down in to the proper spec. 50 ft lbs then backed off twice, then final torque to 75 ft lbs



http://www.ar15.com/forums/t_2_381/215640_.html

http://www.ar15.com/forums/t_3_118/482476_Knights_URX_II_install_______doing_it_the_hard_way__revisiting_the_project_4_9_update_.html

&page=6

http://www.ar15.com/forums/t_3_118/592115_Knight_s_URX_3_1_install.html