Shouldered barrel AR15?

carbonbased · Sep 27, 2025

Go easy on me here.

This is for me to learn why Stoner chose the barrel attachment system he did. Why not a shouldered barrel with internal threads, like on a R700 bolt gun? I mean, as they are, the AR barrel already has a shoulder?

I don’t know much about AR15’s. I do own one, an Armalite, and I like the platform. I’m more of a bolt gun guy.

Never changed an AR barrel, and my entire knowledge of how a barrel mates into the AR receiver is from smilin’ Larry Gdamn Potterfield lol.

Anyway, I couldn’t find an answer online, so I hesitatingly ask you folks.

Edit: is it because of the need to independently orient the gas system? This just occurred to me.

oldrifleman · Sep 27, 2025

I believe it was an attempt to create a fast easy way for “un-Skilled” maintenance teams to easily change barrels. Remove hand guards, unscrew the barrel nut knock out barrel, insert new one, install barrel nut “tighten”, install hand guard, done. The only thing other than bending a gas tube is messing up the barrel nut but that is fairly tough. A screw in barrel you have to break it free, unscrew, insert new one “Torque it down, check headspace and hope. The AR is just more “idiot proof “ with less chance they booger either the barrel threads or receiver threads and mess up headspace.
Not sure how good that worked but it likly ticked off a box on the list of government requirements.

WeR0206 · Sep 27, 2025

oldrifleman said:
I believe it was an attempt to create a fast easy way for “un-Skilled” maintenance teams to easily change barrels. Remove hand guards, unscrew the barrel nut knock out barrel, insert new one, install barrel nut “tighten”, install hand guard, done. The only thing other than bending a gas tube is messing up the barrel nut but that is fairly tough. A screw in barrel you have to break it free, unscrew, insert new one “Torque it down, check headspace and hope. The AR is just more “idiot proof “ with less chance they booger either the barrel threads or receiver threads and mess up headspace.
Not sure how good that worked but it likly ticked off a box on the list of government requirements.

I'm not sure if this makes a difference or not but one other reason for the current setup might be because the receivers are aluminum and the barrels are steel and I wonder if the barrel nut approach is a better way to secure those two different metals together without galling etc.? I've never seen a steel AR-15 upper but if they did make them a shouldered prefit barrel would make sense.

LRRPF52 · Sep 27, 2025

It’s the easiest design to change a barrel on of all military rifles, with very few exceptions. It got away from trunnions, which was a major step in firearms development that many countries still have not embraced. You can’t compete with the AR-10 and AR-15 when it comes to lightweight and ease of armorer serviceability.

XCR and LMT MRP come to mind, both of which are either AR-15 inspired variants or AR-15s, and weigh more.

MO Fugga · Sep 27, 2025

An armorer can be trained in weeks, while it takes years to be a competent gunsmith.

hlee · Sep 27, 2025

MO Fugga said:
An armorer can be trained in weeks, while it takes years to be a competent gunsmith.

Are you saying that I need to send back the certificate I received from YouTube?

LRRPF52 · Sep 28, 2025

MO Fugga said:
An armorer can be trained in weeks, while it takes years to be a competent gunsmith.

Oh the stories we could tell.

I’ve seen ones where the customer’s eyes bulged out of their head upon the “gunsmith” sheepishly revealing the monstrosity to them.

I felt so conflicted with an overwhelming urge to bust out laughing, true mournful empathy with the customer who just witnessed their prized Mauser turned into a colossal abortion, and utter embarrassment for the “gunsmith” who just dropped a deuce in front of his customer.

It’s utterly brutal trying to keep a straight face in such scenarios.

Cascade Hemi · Sep 29, 2025

carbonbased said:
Go easy on me here.

This is for me to learn why Stoner chose the barrel attachment system he did. Why not a shouldered barrel with internal threads, like on a R700 bolt gun? I mean, as they are, the AR barrel already has a shoulder?

I don’t know much about AR15’s. I do own one, an Armalite, and I like the platform. I’m more of a bolt gun guy.

Never changed an AR barrel, and my entire knowledge of how a barrel mates into the AR receiver is from smilin’ Larry Gdamn Potterfield lol.

Anyway, I couldn’t find an answer online, so I hesitatingly ask you folks.

Edit: is it because of the need to independently orient the gas system? This just occurred to me.

The FAL barrel threads into the receiver face, the bolt head spaces from a locking shoulder pressed laterally into the receiver. The barrel is timed by turning back the barrel shoulder with a lathe.

The AR-10 was designed to simplify the assembly and serviceability compared to the FAL and G3.

carbonbased · Sep 29, 2025

Cascade Hemi said:
The FAL barrel threads into the receiver face, the bolt head spaces from a locking shoulder pressed laterally into the receiver. The barrel is timed by turning back the barrel shoulder with a lathe.

The AR-10 was designed to simplify the assembly and serviceability compared to the FAL and G3.

Thanks guys for not making fun of me lol. I’m definitely learning something here.

joe777 · Oct 1, 2025

The barrel extension is essentially the receiver too since it has the locking lugs.

carbonbased · Oct 1, 2025

joe777 said:
The barrel extension is essentially the receiver too since it has the locking lugs.

Ok, next dumb question. I’ve never seen an AR barrel off the gun.

Why have a barrel extension at all? As in, why doesn't the barrel have the extension machined into it? One piece.

Cost? Something else?

Because things that are screwed together in multiple screw-like ways rarely (if ever?) are as solid as a one-piece system with just one large screw. Like a shouldered bolt action barrel.

LRRPF52 · Oct 1, 2025

carbonbased said:
Ok, next dumb question. I’ve never seen an AR barrel off the gun.

Why have a barrel extension at all? As in, why doesn't the barrel have the extension machined into it? One piece.

Cost? Something else?

Because things that are screwed together in multiple screw-like ways rarely (if ever?) are as solid as a one-piece system with just one large screw. Like a shouldered bolt action barrel.

That has been done recently.

It’s all hammer-forged with the extension and gas block integral to the same piece of metal as the barrel itself. All one-piece.

The gas tube has a 45˚ angle to it, as does the gas tube hole in the block. You simply insert the gas tube into the hole with the main length of the tube in the vertical at 90˚ orientation, then rotate it into parallel alignment with the barrel.

Very innovative design. The extension has to be wider than normal though due to the process they use, so it requires a different upper receiver with a larger extension tunnel.

carbonbased · Oct 1, 2025

LRRPF52 said:
That has been done recently.

It’s all hammer-forged with the extension and gas block integral to the same piece of metal as the barrel itself. All one-piece.

The gas tube has a 45˚ angle to it, as does the gas tube hole in the block. You simply insert the gas tube into the hole with the main length of the tube in the vertical at 90˚ orientation, then rotate it into parallel alignment with the barrel.

Very innovative design. The extension has to be wider than normal though due to the process they use, so it requires a different upper receiver with a larger extension tunnel.

Lol I keep missing the billionaire’s parade float.

Funny someone already came up with it. I swear the idea that ideas are in a shared floating quantum soup that we all can taste…sometimes it seems like that soup idea has merit.

roostercogburn98 · Oct 1, 2025

carbonbased said:
Why have a barrel extension at all? As in, why doesn't the barrel have the extension machined into it? One piece.

Some if not all the PCC setups are built that way. The extension is machined as part of the barrel. The Foul Mike Brand upper I have laying in the parts bin was like that. The extension had indexes for aligning the handguard screws.

As stated. Not a new concept, but probably not worth the squeeze with all the extra material you would need for the chamber end of the barrel to be big enough and then have to machine down the rest.

LRRPF52 · Oct 1, 2025

carbonbased said:
Lol I keep missing the billionaire’s parade float.

Funny someone already came up with it. I swear the idea that ideas are in a shared floating quantum soup that we all can taste…sometimes it seem like that idea has merit.

When I was keeping myself occupied in a classroom at Fort Bragg in 1999, being inundated with medical terminology and anatomy & physiology, I drafted out a monolithic upper receiver and quad rail system for the AR-10 that could change between 7.62 NATO and 12 GA. I didn’t have a good solution for the quick barrel change system though, and didn’t have the time to focus on it given the circumstances.

In 2004, Lewis Machine & Tool introduced the Monolithic Rail Platform, but it never generated billions of value, but surely tens of millions when you look all their contracts.

Just between New Zealand and Estonia, LMT sold $59 million worth of MRP carbines.
L129A1 sales to UK for the DMR MWS variant have been 20 million GBP.
LMT just announced a contract to Switzerland as well this Feb:

carbonbased · Oct 1, 2025

LRRPF52 said:
When I was keeping myself occupied in a classroom at Fort Bragg in 1999, being inundated with medical terminology and anatomy & physiology, I drafted out a monolithic upper receiver and quad rail system for the AR-10 that could change between 7.62 NATO and 12 GA. I didn’t have a good solution for the quick barrel change system though, and didn’t have the time to focus on it given the circumstances.

In 2004, Lewis Machine & Tool introduced the Monolithic Rail Platform, but it never generated billions of value, but surely tens of millions when you look all their contracts.

Just between New Zealand and Estonia, LMT sold $59 million worth of MRP carbines.
L129A1 sales to UK for the DMR MWS variant have been 20 million GBP.
LMT just announced a contract to Switzerland as well this Feb:

Didn’t know that’s how their quick change barrel worked, conceptually. Never looked into it. Just looked it up.

Lol man, that’s cool. Made me think of an AI.

For a sec I thought that LMT didn’t use a barrel extension, and I thought, “That’s even cooler.”

Dang.

me now

or maybe this one

LRRPF52 · Oct 1, 2025

Yeah, it’s so simple and effective, very easy to change with consistent torque applied by the provided wrench.

The slot cut allows clearance for insertion and removal, as well as pinch torque around the extension.

If we could go back to Stoner in 1955, sneak into his drafting room, take away his existing drafts, and replace them with that, it would have been really cool for the whole design.

The manual machining technology at the time would have added a ton of time though, with some difficulty in holding the tolerances deep inside the cavity of the handguard.

A semi-monolithic design would have been better, and still allowed use of 7075 forgings on plates, then finish-machined.

It would have set the whole AR-15 family of weapons up better for the variants and ease of maintenance, with inherent accuracy from free-float.

They were big on bayonets at the time though, and there was a misunderstanding that stocks provided some type of barrel support. It hasn’t been until the last few decades that free-floating has become more popular.

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