Can an AR be fired without a barrel nut?

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FrankenMauser

New member
The barrel nut ensures that proper headspace is maintained. If the barrel nut is not present, headspace will become excessive and catastrophic failure is likely to occur.
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The barrel nut simply holds the barrel to the upper receiver.
Headspace is maintained by the barrel extension, which is attached to the barrel.
When an AR is in battery, the bolt is locked to the barrel via the barrel extension.
The upper receiver of an AR is pretty much just an unstressed 'housing' to keep the BCG, barrel, and gas system bits in alignment; and a 'guide' to let the BCG cycle during firing.


If I had random disposable income a video would be forthcoming. But I don't. And I have mouths to feed. So, single rich guys up!
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Not single. Far from rich. Many hungry mouths to feed.
...I just happen to have some AR parts lying around that are either 'expendable' or something that I won't cry over if some risk is taken and an undesirable result is the outcome.

It's a similar story with most of the parts, but... The barrel for this experiment, for example, was purchased about five years ago for $11. I was looking for a "Bubba'd take-off barrel" to cut down to about 10", re-thread, and use with no gas system as a dedicated barrel for the golf ball launcher (on my pistol or SBR lowers).
What I found in a now-closed gun shop was an 18" DPMS barrel that had been drilled into from the bottom, when a Bubba in his garage attempted to remove a gas block in which he had previously applied red Loc-Tite to the set screws.

Bubba didn't set the depth stop on his drill press and created an additional gas bleed hole on the bottom of the barrel. :rolleyes: (And an extremely thin barrel wall where the other screw was drilled out, as well.)

Otherwise, the bore and chamber were in good shape.
The gun shop owner was saving it for the barrel extension, and possibly to be recut as a pistol barrel. He wouldn't take $10 for it, but I met his minimum asking price when I jumped to $11.

Rather than get right to cutting, I decided to test the barrel's performance. First, I pushed some greased lead slugs through the bore, from each end, in order to break any chips that might have been hanging on the new "gas bleed". Then I assembled some 'beater' and spare parts, and that barrel into a functioning gas-less upper receiver.

I fired it as a manual repeater (no gas block) and accuracy was decent enough with factory ammo - about 1-1/4" at 100 yards, I believe.
Then I installed a cheap aluminum gas block upside-down and backwards, to shut off the gas. (Bottom hole blocked by the gas block. Proper gas port sealed with one of the set screws.)
Worked fine. No change, other than the lack of venting gas.

...And stayed that way, because it was brought to my attention that my golf ball launcher was not considered safe to fire on barrels shorter than 16".

But, for testing what my brother refers to as "The Nutless Wonder", I needed a functioning gas system. So, I dug up a spare gas tube, flipped the gas block back around the right way, and located it so that one of the set screws sealed the extra "gas bleed hole" (which, due to the common methods of manufacturing AR gas blocks, meant that the gas block's gas port was also perfectly aligned with the real gas port).

Test firing went fine, with no signs of gas leaks showing on witness paper that was taped in place specifically for that purpose.

And then off came the gas system, off came the barrel nut, back on went the gas system, and it was ready to go.

But, as you'll see in the video, there's a bit more than the typical amount of gas leakage from the gas block, after it was assembled the last time. I do not believe it to be enough to affect operation of the upper; but it did go from zero leaks to more than average. (I use the terms 'typical amount' and 'more than average' here, because I have seen only two or three ARs that didn't have some leakage at the gas block - even if it was only discovered during disassembly or repair, for some reason.)


Anyway... Bottom line: I don't have money. But I do have parts.
 
C

CarJunkieLS1

New member
Ok I'm of the opinion that as long as the barrel stays center inside the receiver and doesn't "cant" itself to prevent a round from feeding, I believe the weapon will fire until the barrel moves out of alignment with the BCG.

Recoil impulse will cause that to happen eventually but how long it may take is anyone's guess. I'm very interested in the outcome.
 
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FrankenMauser

New member
WARNING: The following post includes experimentation with firearms outside of accepted and reasonable limits. DO NOT ATTEMPT any actions discussed or portrayed in this context. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

The first one finally uploaded:

https://youtu.be/x2pLvIUn2WM

More to come (hopefully in a single video), but they aren't ready yet.
 
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FrankenMauser

New member
WARNING: The following post includes experimentation with firearms outside of accepted and reasonable limits. DO NOT ATTEMPT any actions discussed or portrayed in this context. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

For the record, all persons present for testing had eye and ear protection, the rifle was aimed at a safe backstop, and only two of us were 'exposed' to potential shrapnel for the first three test firings. The rest of the witnesses took cover behind a vehicle.

My video editor is having issues again, and I'm tired of fighting it. So, they'll be individual clips.

Initial test:
https://youtu.be/q8oxAGQHQKw


I'm curious whether anyone believes the bipod being clamped to the barrel (via the gas block) would have a notable impact on the results (primarily its additional mass and support point). -- And, therefore, not provide a result representative of a barrel only held in place by the bolt and upper receiver boss.

(Edit: Moved further discussion of the bipod to a later post, as I had the video order out of sequence in my head. Sorry.)
 
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F

FrankenMauser

New member
WARNING: The following post includes experimentation with firearms outside of accepted and reasonable limits. DO NOT ATTEMPT any actions discussed or portrayed in this context. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

Second test: https://youtu.be/ysRl5qtGtYo
 
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FrankenMauser

New member
WARNING: The following post includes experimentation with firearms outside of accepted and reasonable limits. DO NOT ATTEMPT any actions discussed or portrayed in this context. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

Barrel extension area, close-up: https://youtu.be/hk53e7lL8Io

Back to the bipod discussion:

I did not believe it to be a major factor, before the first round was fired; but did wonder if it would skew the result. After subsequent tests, like the first link posted - where we're right next to the rifle - we considered it to be a non-issue.

In this video, you can see the barrel assembly - with the additional mass of the bipod - recoil with the rest of the rifle, and the barrel only moves forward when the BCG comes forward and hits it. The bolt did achieve full lock-up - even though you can't see it in the video - due to the clearances in the upper receiver allowing the bolt carrier to travel farther forward that usual, with the recoil spring pushing the BCG (now locked to the barrel) and barrel assembly forward until the bolt carrier ran into the upper receiver.

The barrel, I believe, would have continued forward, and possibly fallen on the ground, had the bolt not been locked into the barrel extension. But, because it was locked up before the bolt carrier movement was arrested, the barrel comes to a hard stop.

Is the bipod a factor, in my opinion? Certainly.
Is it enough to skew the results? I don't think so.
But I would like to see your opinions.
 
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5whiskey

New member
FrankenMauser you are my hero for doing this. So am I seeing correctly that the rifle was able to chamber another round and go into battery? So it still functioned as a semi-auto? I wouldn't have guessed that.

And FWIW interesting question on the bipod being a factor. I could see it limiting forward movement of the barrel. Time to support it by the lower receiver only for the ultimate test! (I don't think the results will be much different)

EDIT: Now I saw the video from the side showing the barrel coming out some due to chambering and bolt lock-up. Did it still fire without you pushing the barrel/extension back in? Wondering if it moved things far enough forward that the hammer wouldn't contact the firing pin...
 
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FrankenMauser

New member
I figured there'd be a little more discussion before I had to address the elephant in the room. But, 5whiskey, you went right for it...

We were unable to get it to feed a second round. Most of the testing was single-loading.
By the time we got around to trying another round in the magazine, we were low on ammunition and experienced three feeding failures in a row. The cartridges would get partially stripped, and then pinned against the front of the magazine - indicating to me that it was short-stroking. Since it wasn't feeding from that P-Mag, and I didn't want to risk damage to a 'good' magazine, we went back to single-loading.

There was no video of testing whether or not it would feed a second round, as satisfying our own curiosity was the order of the day - not, necessarily, filming to share with other people. If it had worked, we probably would have filmed it. But it didn't...

The bolt did lock open, however, on three or four of the test firings with a magazine in place (to assist loading). So, the short-stroking could have also been an ammunition issue.

I do believe that the second round would have fired, if it had been able to feed. But, of course, we were unable to test that theory without 'cheating' - and there was little point in trying to replicate a condition that the rifle could not achieve on its own.

I need to get that upper back out and test a couple other configurations, and test with a different magazine or two. That P-Mag caused issues with two other ARs that day, and I think it may have been dragging on the bolt carriers in all of them.

Far from scientific testing. But, I worked with what I had available.


(That's not a "beater" or spare parts lower, for the record. That's a good lower - but less valuable to me than my other [better] lowers.)
 
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ed308

New member
Frank, please tell me you weren't the idiot, I mean brave soul holding the cell phone in the video?:)
 
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H

HiBC

New member
Once again,apparently someone does not understand the mechanics of Stoner's AR design.

There are no locking surfaces or lugs in an AR upper receiver. Almost always,when you buy an AR barrel,it comes with a BARREL EXTENSION permanently attached to the threaded,chambered barrel.

The BARREL EXTENSION has the locking lug surfaces machined into it.The Barrel has the chamber machined into it,usually to a nominal depth,and usually to tolerances that will provide proper headspace when matched with a bolt.

For military weapons,the index pin pressed into the bushing is driven in to the point t stakes the barrel to bushing thread in place.The uninformed may see the AR barrel as one piece,but it is an assembly.

Its a good idea to buy a barrel with a matched bolt.The headspace gets checked to that barrel. The receivers and barrel nut might be 1000 miles away,but the headspace is fixed and checked.

The bolt locks into the barrel extension.The relationship between the breech face and and the chamber datum has not one thing to do with the upper receiver or the barrel nut.The actual rifle bolt NEVER TOUCHES THE UPPER RECEIVER,It only touches the barrel extension and the bolt carrier.

To those who insist the barrel nut has something to do with the AR headspace,no offense intended,but you just don't understand the AR.

That's not a problem with us. You might take a deep breath,shrug,and say "Oops!" Its no big deal. That's how we learn.
 
M

Mobuck

Moderator
Since I've personally seen instances in which residual pressure in the gas tube was sufficient to at partially cycle the bolt a second time before it locked up on the next already chambered unfired round, I would say the barrel would be forced out of the receiver before a second round would chamber.
 
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cornbush

New member
Ed308. The idiot wasn’t frankenmauser it was me. This was after being fired several times, I felt comfortable, some may not have but I was fine with it.
 
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FrankenMauser

New member
As cornbush mentioned, several test firings indicated, in our opinions, that the rifle was going to perform as theorized - at least during the initial firing sequence - and remain locked until chamber pressure dropped.

After 4-5 rounds, we weren't afraid to get closer. Cornbush and I were on opposite sides of the rifle for that shot.

Based on the lack of criticism, I'm guessing that no one clicked the playlist link and found the last video clip. ;)


One note on something that I had considered when removing the barrel nut, but then forgotten about until yesterday when I noticed it:
Without a barrel nut in place, the dust cover hinge pin walked out about 3/4" during transport, firing, and subsequent transport. I was surprised that it was still functioning as intended, even though the pin was only supported at the front.

Why didn't I remove the dust cover all together? ...Because, for transportation, the dust cover was holding the BCG in the upper, and the BCG was holding the barrel in the upper. - A delicate dance, but one that worked.
 
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FrankenMauser

New member
Why?
No one is advocating for anyone to perform the activities discussed here.
However, there are certainly plenty of people learning more about the design and operation of the AR-15.

Remember, usually more than 80% of the people viewing a thread never participate in it.

For every person that thought the rifle would instantly explode, there were at least four more that said nothing.
For every person that thought an AR's barrel nut affects head space, there were at least four more that didn't say anything.
For every person that thought this was a dumb idea, but still interesting to see tested, there were at least four more that just sat in the back of the class and didn't participate.

Overall, this thread - though covering a topic with inherent risk, and which should not be attempted by anyone other than professionals - has had primarily positive comments and discussion.

While the topic may be approaching the limit of what should be allowable on TFL, no one is suggesting that the new fad in AR building should be omission of the barrel nut, in order to save weight and make for quick take-down.
This was simply a test to prove or disprove the theoretical operation of an AR, and show that certain parts are 'unstressed' and merely exist to keep the important bits held together and in alignment.
 
J

JohnKSa

Administrator
...residual pressure in the gas tube was sufficient to at partially cycle the bolt a second time before it locked up on the next already chambered unfired round...
Click to expand...
Once the bullet leaves the bore, the gas system is completely open on the muzzle end. Once the bolt carrier moves back about an inch, the system is completely open on the back end. I can't understand how a tube about 18" long could retain any significant residual pressure for any significant amount of time once it is open at both ends--certainly not long enough for the bolt to cycle all the way back and then return forward.

Can you describe the situation in more detail? I can't get a picture in my mind of what's happening from the quoted statement.
 
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Mobuck

Moderator
"Can you describe the situation in more detail? I can't get a picture in my mind of what's happening from the quoted statement"

I acquired an upper that some DUFUS had "built" using a 24" carbine gassed barrel. EVERY shot produced a double feed when the bolt cycled a second time after pushing the first round into the chamber.
An adjustable gas block turned down to nearly nothing sort of solved the problem but still not quite right.
I ASSume you've heard of gas system dwell time. Too much barrel in front of the gas port results in some odd functional issues.
 
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