The FAL Files

The FAL Files (
-   The AR Files (
-   -   Lock nut and lower do not like each other (

raubvogel December 09, 2017 23:03

Lock nut and lower do not like each other
Let's say you have a handguard which has a threaded thingie that goes around the barrel. In the following pict, this threaded thingie (a glorified nut; barrel nut?) is the piece with all the little round holes.
I take the piece being shown with the tool in the same pict is the lock/jam nut for the threaded thingie: once you line up the barrel nut so the gas tube can go through, you then jam the lock nut against the upper receiver.

Am I correct? If so I have a bit of a problem: when the jam nut is tightened against the upper, the lower cannot be placed as it front hinge boss protrudes a bit forward compared to the boss on the upper (this is a set of Palmetto state AR10 receivers, if it matters). So, when the jam nut is jamming, the lowe rboss gets pushed a bit back so the pin cannot line up. I feel like I am doing something wrong here... :facepalm:

Tuscan Raider December 09, 2017 23:09

Ar10. You using the same parts?
They are not universal.

hueyville December 10, 2017 04:47

Have that style of forearm on quite a few AR 15's and AR 10's and never had an interference problem. Above answer may be something to check. Only other solution may be move forearm forward and move jam nut forward and tolerate some threads showing.

OMR_RDTandE December 10, 2017 19:29

If I understand this, the jam nut usually tightens against the hand guard, not the receiver. The barrel nut is torqued to the receiver, holding the barrel in place, and ultimately kept from un-threading by the gas tube.

raubvogel December 10, 2017 19:49

2 Attachment(s)
The handguard I bought is this one (don't remember from where though):

I can't find a proper manual so I am punting here, and apologize ahead of the show. Here are some pictures I took:

First the setup without the handguard in place. The blue arrow is the barrel nut proper, while the green arrow is the jam nut. For me to get the barrel all the way where the the barrel extension is flush with the cutout for it inside the upper, I have to tighten the barrel nut until it sits flush against the receiver (pink).
Once that is done, we can screw in the handguard. I noticed it has a boss on the bottom where you insert an Allen bolt. Am I correct to assume it is there to lock the handguard in place once it is lined up on the top?

If we assume the answer to my question is YES, then it ends up looking like this:
Note the Allen bolt head protruding a bit from under the handguard boss and the barrel nut flush against the lug for the front pin.

Now, even if the jam nut is not there to help lock the barrel nut in place as suggested in previous posts, the barrel nut is still flush against the front pin lug. And the base on the lower does not end flush with the upper lug; it protrudes a bit forward/

hueyville December 10, 2017 21:37

The jam nut does not hold barrel nut snug. Proper torque value of barrel nut holds it. Jam nut keeps forearm snug and as much for cosmetic reasons to hide threads. The set screw aids this as well. W.E.G. would be relieving any area that has interference issues with a dremel. Not that I am recommending that. What pattern upper and what is the brand/model handguard. It may be as simple as a known compatability issue. How about one more picture showing how close or far lower and upper come from lining up? Are we thousandths, hundredths or tenths of an inch from holes lining up so pin fits through both?

raubvogel December 11, 2017 08:46

Upper and Lower are PSA as mentioned in the first post in this thread, which I was told if very DPMS-hy. I do not know if they are PA10 Gen II or I; is there a way to be sure?

The handguard is the one in the link on my last reply. I will try to have a picture showing how inside the hole looks like.

I think this is to show how little I know of ARs. :facepalm:

raubvogel December 12, 2017 07:12

So I did not take the picture yet but have a stupid question: why can't I shove a washer between the barrel nut and the barrel so nut does not need to go flush against receiver to tighten barrel?

jhend170 December 12, 2017 09:51

The holes in the face of the inner nut are meant to be tightened with a free-float wrench to the proper barrel nut torque (35-65lb/ft). Once the barrel is mounted the castle nut is run onto the barrel nut, followed by the freefloat tube. Once you have the tube all the way against the castle nut you then tighten the nut against the TUBE, NOT the receiver. This locks the tube in place without having to tighten it against the receiver. In other words your tightening against the wrong thing in the wrong direction.

Editing: See the studs on the sides of the wrench in this pic? Those are for that type of barrel nut.

OMR_RDTandE December 12, 2017 10:46

These directions are typical for that, and similar type, free-float tubes-

Canuckienns December 13, 2017 00:49

This is Chinese made crap and will never serve you well. I tried this installation for a fellow and it sure aint Yankee Hill.

All times are GMT -5. The time now is 00:38.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
©1998-2018 The FAL Files