M16/M4/M4A1 loose barrels?

[Slater]

Never gave it much thought, but under extended hard use/field conditions are loose barrels an issue? The recent PS Magazine article would seem to indicate that it may be (at least for some units):

"Check for a loose barrel. It’s surprising how many loose barrels we find. A loose barrel kills accuracy"


https://www.psmagazine.army.mil/News/Article/2533441/m16-series-rifle-m4m4a1-carbine-catch-loose-barrels-and-mounting-rails/

[ViniVidivici]

I've never heard of a properly torqued barrel/nut becoming loose through a heavy firing schedule..

How could it, if it's a GI (or comparable type) nut that has the gas tube indexed through the teeth?

I could be way off, but problems as described would, I think, come from improper installation or severe, unusual damage rather than plain hard use.

[lysander]

The handguards of the M4 are keyed and clamped to the barrel nut. Twisting the handguards applies torque to the nut.

You may not think this isn't much, but remember there is a decent lever attached to many handguards, in the form of the front vertical grip. A load of 160 pounds on the vertical grip equals 80 foot-pounds of torque.

The torque should be mitigated by the front handguard mount against the front sight, which is why the article mentions to make sure that is locked in place.

On and one last thing (edit):

The barrel nut does not have to move far to become loose. Even though the gas tube will prevent the nut from unscrewing, it will not prevent the barrel from becoming loose. How many of you have installed a barrel nut? How much rotation is required to go from 10 to 80 ft-lbs? You can do it inside the movement allowed by the gas tube.

[markm]

I've never heard of a properly torqued barrel/nut becoming loose through a heavy firing schedule..

How could it, if it's a GI (or comparable type) nut that has the gas tube indexed through the teeth?

I could be way off, but problems as described would, I think, come from improper installation or severe, unusual damage rather than plain hard use.

Exactly.

[GaWardawg]

I bought a nib colt A4 about 3 years ago. The barrel was loose from factory. I shimmed it to get proper torque. I could twist the hand guards and move the barrel as stated.

[Stickman]

I have personally owned, as well as seen in classes I was teaching, Colt barrels in new weapons which were loose enough to rattle by hand. It is common? Nope, not by a long shot, but it isn't like winning the lottery either. Sometimes the loose end of the torque spectrum gets a little too light when the next notch seems like it might break something.

The morale of the story is to check your equipment, and go over everything when something new is issued to you (or you buy it).

[jsbhike]

I have seen a claim(along with pictures) that an M4 had a barrel nut loose a long enough period of time that the threads wore down enough that the barrel assembly came off the upper.

[utahjeepr]

I'm not saying it doesn't happen but most Colt and FN barrels I have removed have been extremely tight. I mean "stick the upper in the freezer for a couple hours" tight. Sometimes I'm afraid I'm gonna strip teeth off the barrel nut anyway. I swear sometimes that Colt must use superglue on their barrel nuts. ;) (I know they don't really do that, but in the heat of the moment I've called their assemblers some terrible things. :p )

Now mine I could see that as a slight possibility, if i ran standard handguards. I try very hard to stay at the bottom end of torque spec (30lb) on my personal guns. Free float rails index to the upper eliminating that rotation.

In my time in the Corps I certainly never saw that issue, but that doesn't mean it doesn't happen.

[utahjeepr]

Doubled. ?

[1168]

I wonder how many of these were rebarreled, especially given how recently the M4A1 upgrade happened to M4s, and since most M16s still around are ancient. I know that Colt and FN eff up from time to time, but I can see some poor sap rebarrelling thousands of M4s that the Army already had with no torque wrench getting tired of it.

Does anybody know what the logistics were with the upgrade? I never paid attention at the time.

Edit: Feb 2016 is the date on the article. Thats right about the time I started seeing the M4A1 with heavier barrel type in POG and Reserve units. Could also just be the time I noticed, since it was a transition time in my career.

[Wake27]

I wonder how many of these were rebarreled, especially given how recently the M4A1 upgrade happened to M4s, and since most M16s still around are ancient. I know that Colt and FN eff up from time to time, but I can see some poor sap rebarrelling thousands of M4s that the Army already had with no torque wrench getting tired of it.

Does anybody know what the logistics were with the upgrade? I never paid attention at the time.

Edit: Feb 2016 is the date on the article. Thats right about the time I started seeing the M4A1 with heavier barrel type in POG and Reserve units. Could also just be the time I noticed, since it was a transition time in my career.

Pretty sure the entire M4A1 modification was done by civilians, I know ours was. Not that that necessarily means much.

I also know that we just found an upper receiver that wouldn’t fit a new barrel and had no forge markings, so it was assumed that it was an out of spec commercial upper that someone swapped at some point. Sounded weird to me but I don’t know.


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[markm]

I bought a nib colt A4 about 3 years ago. The barrel was loose from factory. I shimmed it to get proper torque. I could twist the hand guards and move the barrel as stated.

Shimmed it? Why not just tighten to the neck tooth notch?