Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
Member Login

Site Notices
1/22/2020 12:12:56 PM
Posted: 11/22/2012 2:50:30 PM EST
This question is dealing with the two piece quad rails that clamp to the barrel nut for their stability on which a fore grip is attached ...

Can these two piece quad rail systems, over time, cause the barrel nut to eventually loosen from repeated firing while tightly gripping the rail its self or an attached vertical foregrip? Although gripping the weapon itself may not cause this over time, couldn't the combination of firing vibrations and gripping the fore grip possibly generate an instance where the barrel nut does come loose over time? Surely over the lifetime of a rifle with a stock hand guard the nut should never come loose, but what about in this situation?
Link Posted: 11/22/2012 2:54:36 PM EST
They usually have anti-rotation tabs, but it really depends on each rail specifically. Which one are you looking at?
Link Posted: 11/22/2012 2:58:13 PM EST
If the barrel nut is coming loose for any reason caused by normal use then it wasn't installed properly to begin with.
Link Posted: 11/22/2012 2:59:36 PM EST
This is something I've wondered myself. Rails such as the KAC Free Float RAS and the discontinued Daniel Defense M4 don't seem to have any anti-rotation measures.
Link Posted: 11/22/2012 3:04:24 PM EST
The anti rotation measures these quad rails have are only to prevent the rail system from twisting and have nothing to do with preventing barrel nut movement (as far as I know).. they rely on the barrel nut for their security on the rifle so any force exhibited to them goes to the barrel nut directly. Am I right?
Link Posted: 11/22/2012 3:08:26 PM EST
Seems plausible, especially if you end up on the lower end of the torque spectrum. I'd like to hear any stories as I'm building another and looking at rails.
Link Posted: 11/22/2012 3:16:36 PM EST
The barrel nut on these systems is the standard barrel nut, which has index slots for the gas tube, which will prevent it from loosening. It's as likely to loosen with those rails as it is with standard handguards.
Link Posted: 11/22/2012 3:28:18 PM EST
Originally Posted By Will816:
The barrel nut on these systems is the standard barrel nut, which has index slots for the gas tube, which will prevent it from loosening. It's as likely to loosen with those rails as it is with standard handguards.


This. While I dont have a standard barrel nut, it is my understanding that once you have the gas tube installed the barrel nut cannot spin unless you shear through the gas tube.
Link Posted: 11/22/2012 4:30:00 PM EST
If you have a 12" long steel VFG I could see how you could "possibly" loosen the barrel nut by twisting the vfg opposite the pistol grip.

But then the handguard/nut would only unscrew enough to contact the gas tube, and the force required to twist the nut past the gas tube would render the rifle inoperable.

I tried to unscrew a KAC M4 rail off a M4 and just ended up breaking the KAC VFG off the rail.

In all reality I doubt a person could un-torque a properly installed barrel nut with a standard VFG, pistol grip, and their hands.
Link Posted: 11/22/2012 4:42:37 PM EST
The gas tube is not going to let the barrel nut to loosen very far. Maybe just rotate a couple of degrees.
Link Posted: 11/22/2012 4:43:03 PM EST
Originally Posted By WI57:
If you have a 12" long steel VFG I could see how you could "possibly" loosen the barrel nut by twisting the vfg opposite the pistol grip.

But then the handguard/nut would only unscrew enough to contact the gas tube, and the force required to twist the nut past the gas tube would render the rifle inoperable.

I tried to unscrew a KAC M4 rail off a M4 and just ended up breaking the KAC VFG off the rail.

In all reality I doubt a person could un-torque a properly installed barrel nut with a standard VFG, pistol grip, and their hands.


There are some proprietary nuts that dont have the gas tube going through them. My Seekins rail has a small barrel nut and the gas tube goes outside of it but it also has anti rotation pins.
Link Posted: 11/22/2012 5:15:35 PM EST
Originally Posted By SteveJbap:
The anti rotation measures these quad rails have are only to prevent the rail system from twisting and have nothing to do with preventing barrel nut movement (as far as I know).. they rely on the barrel nut for their security on the rifle so any force exhibited to them goes to the barrel nut directly. Am I right?


Yeah, but if the rail is wedded to the barrel nut and the rail has anti-rotation, then wouldn't you think that would keep the nut from rotating? If the rail can't move independently of the nut, and the rail can't twist, the nut can't twist.
Link Posted: 11/22/2012 5:28:11 PM EST

Originally Posted By Will816:
The barrel nut on these systems is the standard barrel nut, which has index slots for the gas tube, which will prevent it from loosening. It's as likely to loosen with those rails as it is with standard handguards.

On my MA-TEN build, I used a standard DPMS barrel nut. On the 308 gun, my gas tube passes -above-, not -through- the index slots on the locking nut. As such, the only think keeping my barrel nut from coming loose is the initial installation torque. My Apex FF rail clamps to the barrel nut. I've wondered about this arrangement leading to a loose barrel nut, myself.
Link Posted: 11/22/2012 5:43:13 PM EST
I had an interesting situation occur during the assembly of an upper with an older DD M4 rail, the one with the multi-sided rail locking ring. The barrel nut was proprietary but was designed to have the gas tube go through one of the holes in the barrel nut once timed and assembled. The barrel nut was indeed torqued on the lower end of the spectrum, around 30-35 ft-lbs for appropriate gas tube timing. But once everything else was assembled and it came time to cinch down the rail locking ring with a strap wrench, the barrel nut loosened and was stopped by the gas tube since the direction of the tightening of the rail locking ring was opposite of tightening the barrel nut.

It was a bit of a challenge getting the locking ring loosened at that point and and the rest of the upper disassembled. I ended up timing the barrel nut to the next hole, but this involved getting towards the upper torque limit (likely exceeded the torque range––needed the "gentle" touch of a cheater bar) to accomplish this task. Once done, though, recinching of the rail locking ring did not result in any further barrel nut movement. This was one of the not so fun experiences of building uppers to say the least, and it certainly cast doubts into the design of the FF rails like the older KAC and DD rails.
Top Top