Can an AR be fired without a barrel nut?

[5whiskey]

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

I did. After watching everything else, I would've tried it as well. I bet it could have reliably functioned as a semi-auto handheld, given sufficient rearward pressure on the barrel with your off-hand. Get some asbestos gloves used by Machine Gunners and mortarmen and try it!

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.

Ah, but I'm now thinking that a quick take-down system could be designed easily enough with a torque slip-nut. And I mean by a moderately skilled yet innovative home machinist with a decent home shop. May not be sub-moa accurate, but I bet it would still be much more accurate than your standard Century Arms AK. While I think the armorer manuals for the M4/AR15 weren't written haphazardly, I also think that the torque specs for the barrel nut are quite possibly forgiving.

 

[jdc606]

Interesting experiment that has shown me how unnecessary it is too be overly concerned about specific barrel nut torque settings. Looks like "good and tight" is good enough.

 

[rickyrick]

The barrel nut torque specs are a pretty broad range. It’s to get in the range of “it won’t come loose, but not to tight to damage the receiver”

An experienced technician that turns wrenches every day could hit the mark without a torque wrench.

 

[Unclenick]

What nobody has mentioned is that when the bullet exits it leaves behind a barrel acting as a rocket motor pushing the barrel back into the receiver hard enough to keep it in place and overcome any forward propulsion effort by gas exiting the back end of the gas tube. This continues until the pressure in the barrel drops substantially. After all, not much rearward force is needed. At .224 bore diameter, a residual pressure of just 25 psi would still apply a pound of reward push. It takes a while to drop that low. Over 4 milliseconds.

Disassembly could be expected if you tried to sling it over your shoulder.

 

[FrankenMauser]

I hadn't really considered the "rocket nozzle" effect, but it does seem reasonable. It does, after all, contribute to recoil; and the chamber is 'plugged' by a case.

I did. After watching everything else, I would've tried it as well. I bet it could have reliably functioned as a semi-auto handheld, given sufficient rearward pressure on the barrel with your off-hand. Get some asbestos gloves used by Machine Gunners and mortarmen and try it!

It was fun.
I do not advocate trying such, nor will I say that I intend to do such again.

However, the list for another round of testing includes the following possibilities:
Mandatory: More consistent ammunition.
1. Barrel totally unsupported.
2. Multiple rounds in a better magazine.
3. Bolt locking open if properly supported (not recoiling against a rotting, unstable log).
4. Will it fire after the BCG pushes the barrel forward?
5. Yank on barrel after firing, to show that it's solidly locked.
6. Hand-held semi-auto.

 

[cornbush]

Next time I’ll bring a lancer or GI mag and a supply of known ammo

 

[44 AMP]

Ah, but I'm now thinking that a quick take-down system could be designed easily enough with a torque slip-nut.

The AR already has a quick take down feature, its the TAKEDOWN PINS...

You might come up with a "quicker" barrel change with a slip nut type thing, but it won't be a true "quick change barrel" as found in most belt fed machineguns.

While I think the armorer manuals for the M4/AR15 weren't written haphazardly, I also think that the torque specs for the barrel nut are quite possibly forgiving.

I don't know what the current manuals say, but I can tell you that for Army Small Arms repairmen in the 70s, there were no "exact" specs, The manual said to tighten the nut to 35-40 ft/lbs and then tighten to align the nut to allow the gas tube to pass through,

 

[JohnKSa]

I ASSume you've heard of gas system dwell time.

Gas dwell time is usually defined as the time it takes the bullet to travel from the gas port to the end of the barrel and is the time during which the gas is at high enough pressure to cycle the action.

In the case of a carbine gas system on a 24" barrel using relatively normal ammunition, gas dwell time would be well under 0.001 seconds while it should normally take around 0.07 seconds for the bolt to cycle.

The gas gives the bolt carrier a "kick" that gets it moving, but then very rapidly after that point, the pressure will have dropped. In contrast, it will take around 100 times longer for the bolt to cycle than it will for the gas pressure to drop off.

I don't know for certain why the gun was double-feeding, but I don't see how it could have been residual pressure in the gas system. The pressure in the gas system drops off much too rapidly for there to be any useful amount of pressure in the system by the time the bolt has cycled back forward.

If I had to guess what was going on there, I would say that due to the carbine length gas system on the longer barrel, there was a lot more gas pressurizing the system and that increased the force on the bolt carrier a lot. So the bolt was being flung backwards so violently that it came forward with sufficient force to bounce back off the breechface far enough back to pick up another round. It was probably very hard on the rifle.

This video shows that the bolt can bounce back with defective ammo (this ammo was causing case separations). It stands to reason that if it came back forward a lot harder due to being flung back with a lot more force than usual, it would bounce back a lot more than normal.

https://www.youtube.com/watch?v=aqt9O74nlbA

 

[HiBC]

I have not looked at the book in several years,but in "Black Rifle 2" they discuss buffer development,and "bolt bounce" was a factor

 

[LineStretcher]

As I predicted, someone actually tried it. So now that the "Hold my beer" episode is over and thankfully, no one was hurt, trying to figure out why it turned out the way it did is in fact, very interesting.

For those that feel the basic barrel nut torque specs no longer apply I would agree but only to the extent that the barrel will probably not fall off. I still feel they apply to the point of controlling barrel harmonics. I think most of us understand that repeatable harmonics are the key to improving accuracy.

 

[Joe-ker]

Great thread.

I like the AR and love to learn.

 

[5whiskey]

So now that the "Hold my beer" episode is over and thankfully, no one was hurt, trying to figure out why it turned out the way it did is in fact, very interesting.

It is interesting, and there are further questions that Frankenmauser has asked. Look at it as research. Any designer or manufacturer of a machine has conducted similar testing... on cars, airplanes, right down something as simple as a bicycle. There are parts that are critical for safety, and then parts that are critical for "as intended" function. Doesn't mean the device can't be made to function, as other than intended, without those parts.

As an example, a manual transmission vehicle can be driven functionally with no clutch. It's a drastic inconvenience, just like having to hold an AR together with no barrel nut. It also has it's dangers. It's much more difficult to drive and I wouldn't want to drive one in heavy traffic. But, done correctly and in the right conditions to suit a specific need (like driving it to the shop EARLY when there is no traffic on the road to save yourself a $200 tow bill), it is safe and feasible.

Further, FWIW, lots of guys who collect and shoot WWII rifles must deal with excessive headspace. I would be shocked if even 50% of Arisakas or Enfields won't close on a SAAMI spec field gauge, yet these rifles are still fired by their owners. It helps if you reload, then you can make ammo that headspaces properly to your rifle. Even if you don't, millions of rounds of .303 British have been fired in excessive headspace chambers with users not blowing themselves up. Thanks in large part to factory ammo and published reloading data not trying to reach the gates of hell in loading the round. Further, as a reloader, there are many incidents and examples where I may do something that appears dangerous and against best advice yet is actually perfectly safe. Like swapping Win 760 load data with H 414. Or exceeding some of the more anemic max listed loads of 8mm mauser, or exceeding max listed 45 Colt data for loads that will be shot in a Ruger Blackhawk. While conventional wisdom maybe declare these acts dangerous, a little bit of research and experience deem them perfectly safe within accepted limits.

 

[FrankenMauser]

Indeed.
Know the machine. Know the limits. Understand whether it's an actual risk, or just a departure from standard procedure because you're not dealing with a 'standard' situation.

A Browning Buckmark has grip panels that are critical to retaining full function, but not critical to safety. (They hold some of the parts in place.)
Ruger 10/22s and Marlin Model 60s are similar. The actions will function and fire without the stock, but the stock keeps some of the bits and pieces from falling out.

The top cover is not necessary for an AK-47 to function. But it is necessary for an SKS to function. Different designs, different requirements.


I own a Ruger 77 Mk II in 7x57mm. I will tell you, without hesitation, that I do not stop at published maximum charges with most load data sources. More often than not, I check my usual data sources to see what powders seem to be preferred, and then fire up QuickLoad to see how much better the performance can be while remaining under a pressure level that I feel is safe. ...Because most sources, like with 8x57mm, limit their data to somewhere between 36,000 psi and 42,000 psi; even though SAAMI MAAP is 51,000 psi.

I know the cartridge can handle it. I know the rifle can handle it.
BUT I do that ONLY for that rifle. I have other 7x57mms here, and I do not believe that they could handle full power ammunition for very long. They get anemic, low pressure ammo that is loaded specifically for those rifles.

The 77 Mk II gets ammo loaded and marked specifically for it. The others get ammo loaded and marked specifically for them. And, loaded to the "lowest common denominator", at that - a 1916 Spanish Mauser.

(The 77 Mk II 7x57mm has a "twin" that lives right next to it in the safe, chambered for the 65,000 psi .270 Win. ...But I do NOT exceed trustworthy published max loads there.)


Know the machine. Know the limits. Understand what you're dealing with.

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It has been suggested that the 'fired without a barrel nut' concept be applied to a Savage-style rifle, with the threads removed. -- In essence, a smooth receiver ring and smooth barrel shank, with no means of mechanically locking the barrel into the receiver. The idea being to test Ackley's theories of chamber friction and bolt thrust.
But I don't see anything good in a test like that. All I see is case failure and unnecessary risk of personal injury.

 

[5whiskey]

But I don't see anything good in a test like that. All I see is case failure and unnecessary risk of personal injury.

I see the same thing in such a test. Those theories could be tested in a much safer manner. Like setting the headspace of a savage rifle long (say .010) and placing lead shims between bolt lugs and action lock. Measure your shims before and after. Case failure is much less likely, but I would wager the lead shims are compressed a fair bit.

 

[JohnKSa]

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.

Thinking about this more, I'm not fully satisfied with my earlier analysis. I'm trying to understand how the bolt could have bounced back and left the live round in the chamber instead of extracting it.

 

[FrankenMauser]

Thinking about this more, I'm not fully satisfied with my earlier analysis. I'm trying to understand how the bolt could have bounced back and left the live round in the chamber instead of extracting it.

I've been trying to remain quiet on the subject, but also have some doubts.
A live round being chambered and then the BCG recoiling again to 'double feed' seems ... 'difficult'.
But, a live round being chambered, at all, in a system that still has enough residual pressure to cycle the BCG again is what I really cannot fathom.
If there's enough gas pressure to (even partially) cycle again, there's enough gas pressure to keep the next round out of the chamber (and the bolt carrier's gas key from covering the gas tube again).

(Yes, I dropped the contraction [can't] in favor of the full word [cannot] {but not "can not"}, simply because of the use of the word 'fathom'.)

I see the same thing in such a test. Those theories could be tested in a much safer manner. Like setting the headspace of a savage rifle long (say .010) and placing lead shims between bolt lugs and action lock. Measure your shims before and after. Case failure is much less likely, but I would wager the lead shims are compressed a fair bit.

Not a bad suggestion.
But it wouldn't achieve a result "spectacular" enough to be worthwhile.
Measuring lead shims - which I do have - is boring. Seeing a barrel fall out of a rifle is impressive/entertaining.

(I do have rifles suitable for such testing. I just don't want to...)