DIY Magpul UBR Installation Question

AR/M4 AR General Discussion
1

This may seem like a dumb question, but since many people have done their UBR installations themselves, I thought I’d ask it anyways…

How important is it to properly torque down the entry receiver extension with the UBR to the specified 35-39 ft/lbs? Is “hand-tightened” good enough? I’m attempting to install a UBR to a lower and I don’t have a torque wrench.

If one is absolutely required, what’s a good, cheap place to buy one, and how do I get the socket-style attachment to fit the back of the receiver extension?

Thanks!

2

Hand tightened is not, IMHO, good enough. The torque settings are optimized to prevent back-out or loosening under repeated recoil.

As far as buying cheap, I would shy away from that approach and instead invest a little in a good quality tool with an iron-clad lifetime warranty like Craftsman or Snap-On. Lowe’s ad Home Depot have their store brands (Husky and Kobalt respectively) that are well made and offer good replacement coverage as well.

The receiver extension tube “socket” is not available as a part in and of itself, but instead is part of a tool like the RRA castle nut wrench. You simply place the square tool end of the torque wrench into the appropriate cut out on the tool and use the cut out that fits on to the receiver tube end. Easy as can be!

Good luck!

3

You can rent a torque wrench from Auto Zone for free (You have to put down a $100 refundable deposit)

4

I have hand tightened 3 of them now, never had a single problem with any of them and one of my goes back to the preproduction models

I should add that I did use a wrench to do it but just did not go crazy on them. It was not a torque wrench.

5

I went and idiot-gorilla’d mine in, and have had zero problems as well.

6

You don’t need a torque wrench. Tighten it by hand. Then use a wrench and snug it up good. If you do everything correctly it won’t come loose.

7

I hand tightened with some blue loctite. 4000+ rounds so far, 2000 of those this last weekend at a course.

8

I am glad it’s working for you, but Loc-Tite is the wrong answer.

9

I’m sure that Mr. Murphy can strike at any time, but the UBR extension isn’t like a carbine receiver extension.

I guess the screw at the back could loosen and let the extension start to rotate, but that stock would start to feel all kinds of funky and loose fast.

I’ve never heard of a UBR loosening- has anyone?

What is the Mark 1 Mod 0 spec for hand tightening?

10

IG could you please expand on this a little further. I agree that proper torque is the answer but it seems like loc-tite on something you don’t want coming loose could only be additional insurance?

11

I have installed 3 UBRs. All 3 were tightened by hand via a large flat bladed screw driver. I have not experienced any issues with the receiver tube screw working it’s way loose. The most recent UBR stock came from MagPul with quite a large amount of dried blue loctite pre applied on the receiver tube screw.

12

Mine came like this as well. I used a large screwdriver with some pliers for extra leverage.

13

I was referring to putting Loc-tite on the threads of the actual receiver extension. I used it on my screws.

If you have ever had to break a lower receiver extension loose that has been Loc-tited you’ll understand what I mean.

14

I wasn’t talking about putting loctite on the extension, just the screw.

15

I would hazard a guess that gas-key screws and receiver extension nuts are staked in place because when you are in the middle of a 72-hour or longer mission, having your rifle go tango uniform isn’t going to be an acceptable excuse. In civilian life, you can notice the nut becoming loose and you can get it fixed that day, or at most the next morning. That doesn’t happen often during conflicts. Nuts and screws are staked in anticipation of a worst case scenario.

Most of us probably have a set of hex wrenches, screwdrivers, maybe some punches, an extension nut wrench within either an arms reach or at home. That’s maintenance prohibited at the user level in the military.