Can an AR be fired without a barrel nut?

[FrankenMauser]

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.

Can an AR be fired without a barrel nut?

This is a follow-up to my snarky reply to a typographical and/or grammatical error (or plain old brain fart) posted in a previous thread, by another member.

I want your thoughts.

Will it fail to fire?
Will the barrel fall off?
Will the case rupture?
Will it work just fine?
Will the barrel extension and threaded receiver boss explode, due to being unsupported?
Will the ... fill-in-the-blank ... cause ... fill-in-the-blank ... to ... fill-in-the-blank?...?

What will happen if an AR is fired without a barrel nut?


I can not lie. I must admit now that, perhaps surprising, video is forthcoming.

 

[HiBC]

I'm not going to draw pictures or think too hard.

It seems to me if you juggle all the parts just right,you might be able to assemble everything with the BCG in battery and a round in the chamber,


It should go "bang" once. What happens next? Depends on any friction or loc-tite between the barrel extension and the upper.


While the BCG is out of battery and in the recoiling/feeding stages I don't see anything else holding the barrel in the upper,except maybe the shooter's hand.

Chambering might eject the barrel.

Lockup is bolt to barrel extension.Barrel nut is not resisting chamber pressure.

 

[Elkins45]

If you hold the barrel in place while chambering the round it will fire. The bolt will hold the barrel in place while the hammer drives the firing pin forward.

All bets are off for the second round. Depending on how much friction there is between the barrel extension and the receiver the next round might drive the barrel forward out of the receiver.

 

[LineStretcher]

There is only one answer. It will immediately make the person trying it stupider than they were before the tried it.

The question is not a very responsible one since someone may actually try it just to see what happens. DO NOT DO THAT!!!!!!!!!!!!!!!!!!!!!!!!

 

[JohnKSa]

Ok, I'll play.

To be clear, I'm just thinking this through. Nothing below should be considered to be an endorsement of the practice or a guarantee of safety.

The bolt locks securely to the barrel so there wouldn't be any danger of things coming apart until after the bolt unlocks.

There's a good bit of friction between the barrel and the bullet so there will be forward force on the barrel upon firing; however the bolt won't unlock until the gas unlocks it and that will hold the barrel on. No gas will flow to unlock the bolt until the bullet passes the port in the barrel.

After the bullet passes the port, the gas will begin to flow back through the tube--at a higher velocity than the bullet. But the bullet has a shorter distance to travel to exit the barrel after passing the gas port than the gas has to travel back to the bolt.

Once the gas gets to the bolt, it will begin the process of unlocking the bolt. That will take awhile (in bullet time) so I'm guessing that the bullet will be well out of the bore before the bolt fully unlocks from the barrel. Not only because that seems about right, but also because it's probably a design requirement to insure that the bolt stays locked until the bullet exits for safety reasons. The pressure in the bore/chamber needs to have dropped to next to nothing before the bolt opens to keep bad things from happening

Once the bullet exits the bore, there's no longer anything pushing the barrel forward so there wouldn't be any reason for it to come off then.

When the bolt comes back forward, the bullet feeding process will push the barrel forward somewhat, but not much--the shooter's hand on the forearm should be able to easily keep it in place. Then once the bolt locks, we're back to the starting position--the barrel isn't going anywhere with the bolt locked into it.

 

[FrankenMauser]

Good replies.

JohnSKA, in particular: Great theoretical analysis.

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.

My own theory followed that train of thought. Boiled down to its most basic form: The bolt can't unlock while chamber pressure is high. And if it can't unlock at high pressure, there shouldn't be a problem.

But, even while believing that theory, I still wondered about the post-unlocking sequence.
Will the residual gas pressure forcing the bolt open and bolt carrier rearward be enough to push the barrel forward? (Via the gas tube and gas key interface, not residual bore pressure.)
Even if the barrel remains stationary during the recoil phase, will it be able to remain in place when the bolt comes forward again? Or will the bolt (or BCG as a whole) push the barrel right out of the receiver?

We did test the basics.
Some of our questions were answered. Others were not (proper test scenario not possible, or we didn't think to set things up for it at the time).
I'm still waiting on a few video clips from one of the experiment's participants. Once I get that, I'll get the video(s) posted as soon as I can.

 

[JohnKSa]

That's significantly more stress than the bolt was designed to withstand.

The stress on the bolt should be identical in either case. In both cases the bolt is holding closed under the stress of firing and is locked to the barrel. During the locked phase, the bolt and barrel don't "care" about anything other than each other and that remains true regardless of what they are connected to--or aren't connected to.

Will the residual gas pressure forcing the bolt open and bolt carrier rearward be enough to push the barrel forward? (Via the gas tube and gas key interface, not residual bore pressure.)

My gut feel says no it won't. By the time the bolt unlocks, there should be very little residual pressure in the gas system because there's nothing containing it on either end. The bullet is gone out of the bore so there's no containment on that end, and after the gas "kicks" the bolt carrier back the gas will vent into the receiver on that end.

Even if the barrel remains stationary during the recoil phase, will it be able to remain in place when the bolt comes forward again? Or will the bolt (or BCG as a whole) push the barrel right out of the receiver?

In my mind, this is the big question. I don't own an AR so I can't pull it out to look at. I think if a shooter were holding the forearm normally, that would provide enough force to hold the barrel in place. But fired in a fixture? I just don't know.

I'm really interested to see the video results!

 

[44 AMP]

-the shooter's hand on the forearm ...

If I know there is no barrel nut, then my hand isn't going anywhere NEAR the forearm.

OK without a barrel nut, how do you get the slipring, spring, and handguards to stay in place?

Theory says everything will stay together for firing, and I think it unlikely the reloading cycle will push the barrel (and everything on it) out of the upper. But I think it likely that, with no barrel nut, it might push it forward enough to upset proper feeding and full lock up of the bolt. And I don't think hitting the foreward assist would be all that useful, either...

 

[JohnKSa]

Forgot to include the caveat in my second post that I was just trying to think things through, not suggesting that someone should actually try this.

 

[ed308]

Who's starring in the video? Johnny Knoxville?

 

[FrankenMauser]

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.

Who's starring in the video? Johnny Knoxville?

I'm sorry to disappoint, but the star of the show was a 20-foot length of 550 cord ... and a notable appearance by a rotting log.

My father (not a participant) was present. He asked, "What's the point of this?"
"Knowledge and enlightenment," I replied.
"'Lightenment' ... ... ... sounds like an ice cream cone would be a better use of your time," he replied.

He was, however, very interested in the testing, and even pulled the cord [trigger] for two shots. (Yes, it survived at least two firings.)

Forgot to include the caveat in my second post that I was just trying to think things through, not suggesting that someone should actually try this.

Indeed.

Further warnings will be forthcoming; but, under absolutely no uncertain terms should such actions be attempted by anyone. Any attempts to fire a rifle in an incomplete configuration are absolutely insane.
Do Not Attempt.


(Warning to be added to previous posts.)


Man... I need that video. Waiting on email!...

 

[HiBC]

Actually,the gas tube is attached to the barrel.Gas tube will give a little push to the barrel

The gas pulse is contained in the BCG by the rings.So the bolt/BCG are essentially an air cylinder that gets a little longer.

The BCG mass is accelerated rearward,but it would seem to me the same force would try to accelerate the barrel(actually,bolt in battery) forward.


Its not about lockup and chamber pressure,the barrel nut has nothing to do with that.But the forces of gas operation should find the path of least resistance.


The pressure in the BCG blows the BCG to the rear with the same force it wants to blow the bolt out the front.The bolt is resisted by the barrel.


I think some cycling force will want the barrel to move forward.


It is an interesting puzzle

 

[LineStretcher]

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.

You all can theorize what might happen and that's pretty cool but there's some well known facts that say exactly what might happen. We would not have head space knowledge if someone had not already done testing so no need for anyone here to try it.

 

[HiBC]

The barrel nut ensures that proper headspace is maintained.

That might be true with a Savage bolt gun. Its not true with AR type rifles.

The locking lugs are in the barrel extension.You don't need an upper reeiver,or a barrel nut,to check headspace with an AR barrel (with extension),a bolt,and headspace gauges.

 

[LineStretcher]

That might be true with a Savage bolt gun. Its not true with AR type rifles.

The locking lugs are in the barrel extension.You don't need an upper reeiver,or a barrel nut,to check headspace with an AR barrel (with extension),a bolt,and headspace gauges.

This is a really stupid subject and I can't believe I'm even participating.. I'm out. Blow yourselves up if you want. I'll send your family a condolence card.

 

[rickyrick]

I think that the first round would fire just fine. After the bullet passes the gas port I’m not sure what would happen. But I’d predict that the barrel will have some forward movement depending on the weight of the barrel. It’s all gonna get pushed apart when the gas system gets involved.
I think if the gas system is disabled, and the cartridges are manually loaded carefully, it could fire many times. I wouldn’t try it if it auto loaded the cartridges.

But I wouldn’t try it or recommend it, but based on how the bolt and the barrel extension interact with each other, I think it would fire if carefully loaded

 

[stinkeypete]

This isn’t a stupid topic. It seems to me it is one extreme in testing “what is the effect of the barrel nut tension on an AR.”

As usual, I did something bass ackwards.

I built a sun MOA ar 15 varmint rifle about 18 years ago. Rock River 24” bull barrel, bolt and carrier group, RRA 2 stage trigger, and the rest is just common parts. A big Swift scope. It took more time to decide which parts I liked than it took to assemble the rifle.

My first trip to the range got my handloads close, the next week I zeroed in on a very good load and the third week I was shooting 10 shots under a us quarter over and over again. I thought getting sub moa was going to be a good hobby but I was done.

Recently, I started shooting .22 LR rifles... a cz and a Dick’s $200 10/22. I wondered what I could do to make the 10/22 really drive tacks. Out of the box, a 10/22 is certainly a very capable plinker or hunting rifle, but on the bench..... let’s just say I have learned a lot and have many rivers yet to cross.

The point:

An AR varmint rifle is spooky accurate. I mean from my recent experience, I am looking at every element and comparing between the AR and 10/22 platform to see why the ar platform is so crazy good.

The role of the barrel nut isn’t trivial, just because it’s been done in a way that in retrospect to me seems genius.

“What is the role of barrel nut torque”... connecting aluminum to steel and holding the free float forearm on...” well, one logical (but not practical) question is “what if it wasn’t there?”

The proof is in the pudding.

 

[5whiskey]

This is a really stupid subject and I can't believe I'm even participating.. I'm out. Blow yourselves up if you want. I'll send your family a condolence card.

I don't believe being inquisitive with a measured approach to safety is stupid at all. It's a question posed. No one is saying someone should go drink a case of beer, try this, and film it with a phone camera this weekend with no safety measures taken. If you knew how to assemble an AR upper, you too would be assured that anyone who tried this wouldn't "blow themselves up." They may damage their equipment, and there is a remote chance of ancillary injury by a barrel careening off the front of the gun (most likely outcome IMO), but the rifle won't explode. As HiBC said, a barrel nut has nothing to do with headspace on an AR. Once the round is actually chambered, the bolt is locked to the barrel extension. It is as safe to fire as it would be with the barrel nut in the context of case head support.

Will it fail to fire?
Will the barrel fall off?
Will the case rupture?
Will it work just fine?
Will the barrel extension and threaded receiver boss explode, due to being unsupported?
Will the ... fill-in-the-blank ... cause ... fill-in-the-blank ... to ... fill-in-the-blank?...?

Let's assume you have ensured that there is a round chambered and the bolt is in battery. It would maybe require you to hold the barrel to keep it from being pushed out of the receiver as the round chambers. Once at that point...

Will it fail to fire? Maybe. I don't think so but there's a remote chance the hammer hitting the firing pin would push the whole barrel/bolt/carrier assembly forward. I think the mass of the barrel would hold it in place well enough for the primer to ignite.

Will the barrel fall off?This is the most likely adverse affect, is that the barrel falls off to the front. It should be safe until the bolt unlocks as pressure will push the bullet down the barrel, but it will also push back on the bolt holding it in place. Once the bolt unlocks there is a chance that the gas pressure will push the bolt carrier back along with pushing the barrel forward... possibly enough that it falls off the front. I don't know for sure.

Will the case rupture? No, the case is completely supported by the bolt locked into the barrel extension.

Will it work just fine? To get one round downrange, after it was chambered with aid, likely. I believe that the barrel may fall off (or at least be moved forward in the receiver) once the bolt unlocks, but if not then almost definitely when the bolt pushes the next round onto the feedramp.

Will the barrel extension and threaded receiver boss explode, due to being unsupported?No the chamber is bearing that outward pressure during the firing of the round. The only pressure on the barrel extension is rearward via the bolt locking lugs engaged with the lugs in the extension.

Will the ... fill-in-the-blank ... cause ... fill-in-the-blank ... to ... fill-in-the-blank?...? My guess is you aid in chambering one round, it fires, and when the next round is stripped from the mag and hits the feed ramp it will shove the barrel forward some, which will absorb enough energy that the bolt will never go into battery with the new round.

Looking at it, rotational force placed on the barrel due to rifling could also cant the barrel and bind it so that the bolt may not unlock properly (or really at all). I now have a strange desire to see this done. 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!

 

[5whiskey]

I think if the gas system is disabled, and the cartridges are manually loaded carefully, it could fire many times.

I believe this to be accurate as well.

 

[Elkins45]

Looking at it, rotational force placed on the barrel due to rifling could also cant the barrel and bind it so that the bolt may not unlock properly (or really at all).

No, there’s a pin that indexes the barrel extension in the upper that would prevent rotation.