From A Technical Perspective: Why Mil-Spec Vs. Commercial Buffer Tube?

[Kronos451]

Can someone please enlighten me as to why a mil-spec buffer tube is considered to be so much better than a commercial tube? It seems to me that the only real difference is in the cost and method of manufacture, but I'm always open to having my paradigm shifted. I looked for this topic in the forums but haven't been able to find it. Also -- I have my Kuhnhausen books for my 1911 work, but what is the AR equivalent to those seminal tomes? Thanks in advance for reasoned, well-thought-out and well-intentioned replies...

Kronos451

[danco]

I believe it has to do with the rolled threads on the mil-spec RE, compared to the cut threads of the "commercial" tubes.

When a mil-spec RE is threaded, material is displaced from the root of the threads that then becomes the crown of the threads, with an increased outer diameter greater than the tube's OD. Commercial tubes with cut threads are thicker to account for the material that gets cut-away during threading.

Many prefer the rolled threads of the mil-spec tubes because, in theory, they are stronger (in tension, shear, and fatigue resistance) because of the work-hardening that occurs when the threads are rolled.

~Dan

[Eric D.]

I seem to recall it being said that the threads on a commercial tube aren't cut to a full height (maybe 50-60% thread if i had to wager a guess) and there are reports of commercial tubes pulling the threads out of lower receivers.

A true mil-spec tube is also made from a 7075 extrusion. Most commercial tubes and many claiming to be "mil-spec" are made from 6061 extrusions.

[Suwannee Tim]

...Also -- I have my Kuhnhausen books for my 1911 work, but what is the AR equivalent to those seminal tomes?....


Count me in on the book question.

[JohnnyC]

I think part of the problem is the varying tolerances in commercial tubes. Since there's no spec for commercial tubes, things need to be made looser with sloppy tolerances. This along with the other things mentioned means it's just not worth it to dick around with.

[Bob Reed]

A true mil-spec tube is also made from a 7075 extrusion. Most commercial tubes and many claiming to be "mil-spec" are made from 6061 extrusions.
Genuine COLT Receiver Extensions are made from Hammer Forged 7075-T6 Aluminum http://www.specializedarmament.com/products/RECEIVER_EXTENSION_CARBINE-144-4.html

And this is another one of the many reasons why Genuine COLT Parts are better than the "other guys".

[scoutfsu99]

Stick with quality components and good companies.

BCM - http://www.bravocompanyusa.com/Milspec-Receiver-Extension-Buffer-Tube-p/bcm%20milspec%20receiver%20extension.htm

COLT - http://www.gandrtactical.com/cgi-bin/commerce.cgi?preadd=action&key=M4RE

COLT - http://www.midwayusa.com/product/964209/colt-receiver-extension-buffer-tube-post-ban-compliant-mil-spec-diameter-ar-15-carbine-aluminum-matte

[VIP3R 237]

Another reason to prefer mil spec over commercial is EVERY aftermarket stock manufactuer will make a milspec stock and when a new design comes out it will be availiable in mil spec first. Not so much on the commercial side but it is getting better

[francobx22]

Stick with quality components and good companies.

BCM - http://www.bravocompanyusa.com/Milspec-Receiver-Extension-Buffer-Tube-p/bcm%20milspec%20receiver%20extension.htm

COLT - http://www.gandrtactical.com/cgi-bin/commerce.cgi?preadd=action&key=M4RE

COLT - http://www.midwayusa.com/product/964209/colt-receiver-extension-buffer-tube-post-ban-compliant-mil-spec-diameter-ar-15-carbine-aluminum-matte

agree with this one

[Clint]

Can someone please enlighten me as to why a mil-spec buffer tube is considered to be so much better than a commercial tube? It seems to me that the only real difference is in the cost and method of manufacture, but I'm always open to having my paradigm shifted.
Kronos451

Good question.

AFAIK,
true mil-spec extensions are made of 7075 aluminum alloy using the impact extrusion process.

commercial extensions are made of 6061 aluminum alloy using the conventional extrusion process.

7075 alloy is approximately 66% stronger than 6061.

7075 cannot be readily ram extruded like 6061 can.

7075 can however, be forged and impact extruded WIKI (http://en.wikipedia.org/wiki/Impact_extrusion),MUELLER (http://muellerindustriesipd.com/category/impact_technical_information).

Impact extrusion is a lot like forging, but the material flows more.


The insides of quality extensions are also coated with a dry film lubricant WIKI (http://en.wikipedia.org/wiki/Dry_lubricant), SANDSTROM (http://www.sandstromproducts.com/),
which makes them conducive to smooth cycling.

Cheaper extensions that skip this critical step feel gritty.


So, the difference is primarily a material, strength, process and coating issue.

I would never buy a commercial tube.

Quality and performance is key.


You can add VLTOR to the above list.

[Pax]

Genuine COLT Receiver Extensions are made from Hammer Forged 7075-T6 Aluminum http://www.specializedarmament.com/products/RECEIVER_EXTENSION_CARBINE-144-4.html

And this is another one of the many reasons why Genuine COLT Parts are better than the "other guys".

You have any more reputable source, perhaps something released by Colt themselves? A few minutes of searching on my part has turned up no such thing as a "hammer forged" RE, but I could be wrong.

[Robb Jensen]

Personally I only use REs from BCM, Colt, LMT, KAC, DD and VLTOR. Everything else is suspect.

[DirectDrive]

I think part of the problem is the varying tolerances in commercial tubes.
This from personal experience.
Also I believe that since a fighting gun's stock might have to be used as weapon, (or other severe service) the receiver extension must meet the higher standard.

[markm]

Search "Buffer Tube Basics" as a thread title.

There's absolutely NO REASON to run a Commercial piece of shit. A decent part is only usually $20 more.

Even amongst the "mil spec" REs there's a pecking order. I have some rough ones. REAL Colt REs will have a mirror smooth finish inside that you can actually hear and feel when cycling the charging handle.

[JSantoro]

Reading the stickied threads at the top of this subforum would have netted this: https://www.m4carbine.net/showthread.php?t=7009

...which contains the thread markm specified, among others that contain answeres to many, many general technical questions.

Between that and Clint's post, this one's pretty well answered. Again. :D