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Mil Spec vs. Commercial AR 15 Buffer Tubes – Which One is Better?

This is one of the most common questions we are asked, and for good reason. If you are interested in upgrading your AR-15 stock, or planning to build an AR, it is critical to understand the subtle differences between mil spec buffer tubes and commercial AR 15 buffer tubes two very similar standards.

Understanding Mil Spec Buffer Tubes vs. Commercial AR 15 Buffer Tubes

Buffers, Tubes, Stocks, and Springs: Definitions

AR 15 Buffer Tubes

The AR-15 buffer tube (also known as the receiver extension), is the metal protrusion that sticks out of the rifle and serves two functions: it houses the recoil buffer mechanism, and it serves as the attachment point for the buttstock.

The reason it’s referred to as a “buffer tube” is because inside the tube is a large spring (called the action spring), and a weighted part known as the “recoil buffer”.

More info: When the rifle is “cocked” using the charging handle, the action spring is what makes the bolt slide back forward. Also, after a round is fired, the action spring is what pushed the bolt back forward and chambers the next round. The recoil buffer sits inside of the spring, and its weight provides some “buffer” against the forces of recoil. By changing the weight of the buffer, you can change the characteristics of how the rifle cycles.

Difference between Mil Spec Buffer Tubes and Commercial Buffer Tubes

Now that you know what’s going on inside the tube, let’s examine the difference in types.

The most critical difference is the diameter of the area where the stock slides onto the tube. The mil spec buffer tube is about two hundredths of an inch smaller than commercial. This may not sound like much, but it’s enough that buttstocks designed for one standard will not be compatible with the other.

There are other differences that people will point out, such as the angle of the back of the tube, or the type of metal used. The problem is – these traits can vary by manufacturer, and are not necessarily related to the diameter of the tube.

More info: The below picture shows the different dimensions of the 2 items
Cross Section of Milspec versus Commercial AR 15 Buffer Tube

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I’m looking to buy a new buttstock. How can I tell which size I need?

As we mentioned above – you need to match the stock to the buffer tube. Most stocks come in both mil-spec and commercial varieties.

The best way to measure is by using a micrometer, and measuring the diameter of the tube. A mil-spec tube should measure about 1.146”, and a commercial will be about 1.17”.

Why do 2 different standards exist?

As with so many things – it all comes down to money. The mil-spec buffer tubes were the original design, but the manufacturing processes of commercial spec buffer tubes provide a lower cost.

More info: When the M4 was first introduced as a military weapon, there was only 1 type of tube – mil spec. But as the M4-pattern rifles moved into the civilian ranks, companies realized that they could make the tube cheaper. By making the tube a touch larger in diameter, the threads could be cut in, vs the mil spec tube where the threads are rolled in.

So which one is better – Mil Spec or Commercial?

First off – we cannot find any scientific evidence supporting that one standard is noticeably “better” than the other on strength, performance, etc. But we recommend using a mil-spec buffer tube.

Why? Even though it costs a little more, there are more options for aftermarket stock upgrades, and many people believe that the part is slightly stronger (again, this lacks the scientific proof we would like to see).

More info: We see increasing movement toward this becoming the “standard”, in spite of the fact that it tends to costs more. No doubt, the fact that the military favors this standard is a big part of this. For instance, Magpul recently reduced the number of commercial spec stocks that it offers, and now only offers most commercial stocks in black.

One Last Tip

If there’s anyone that knows the AR-15 platform, it’s the US military. As a special offer for our readers, you can get the Official US Army Manual for AR-15/M4/M16 right now – for free. Click here to snag a copy.

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19 thoughts on “Mil Spec vs. Commercial AR 15 Buffer Tubes – Which One is Better?

  1. i have a commercial buffer tube assembly on a ar 15. is there a conversion kit to go to
    the mil-spec system?

    1. Yes. Buy a Mil-spec buffer tube. You cannot shrink the aluminum tube down.

  2. Hi Derrick, the only thing you need need to replace is the buffer tube itself. The spring, buffer, and other parts are all interchangeable. Something like this would work:

    1. Hi,
      so… if I’ve bought an M4 with a native commercial tube, and I would like to change it with a Mil-spec tube, the lower will accept the new tube?
      The threads is the same?

  3. If the difference in tube size is actully about .020″. then the 1st comment is true. Otherwise the difference would be .054″.

  4. You ask for proof for one over the other.
    Rolled threads (mil spec) are stronger that cut
    Threads, especially on such a thin walled tube.
    40 year machinist

  5. Another comment regarding strength, Mil-Spec buffer tubes are available in 6063 T6 aluminum alloy and 7073 T6 aluminum alloy. 7073 is roughly twice the strength of 6063, for that reason it’s marketed as Heavy Duty when choosing buffer tubes. A 7073 tube will cost more than a 6063 tube. Commercial buffer tubes only come in 6063 T6 alloy. Whether you’re building or trading out parts, one should ask themselves what level of activity you’re going to engage in, and how muvh potential abuse will the stock receive. If it’s going to be used and potentially abused in the field, go for the heavy duty 7073 tube. If it’s your blanket darling and only fired at the range, then go with the cheaper 6063 tube.

    1. The Alloy’s are 6061-T6 and 7075-T6 Aluminum. You need to get your numbers right. However, I somewhat agree with your comment. For as little difference that there is between the two Alloy’s in cost, I would suggest that you always go with the 7075-T6. Because the bottom line is that regardless of why you built your new baby it should always be up to the task of taking a beating. You never know where life will take you and that little number between the two could be the difference between a go/no-go situation. Is it really worth it to save a few dollars. Not in my world.

  6. Will the mil spec kit fit on a Windham AR 15? Or when u go to purchase online do u need to know what ur gun will hold size wise?

    1. Yes

  7. I am building a .458 SOCOM. Do I need a heavier buffer spring and buffer than the standard AR-15 Mil Spec Buffer Tube Assembly?

  8. I mean sure, it had nothing to do with creating a competing standard to F! people over…. right?

  9. Do they make a rifle length tube that is mil-spec that a mil-spec buttstock will fit on?
    Jim Jinks

  10. I was always wondering why my buttstock was loose on my ar build. Measured both and found buffer tube was mil-spec and buttstock commercial.

  11. If I have a mil-spec lower receiver, can I screw on a commercial receiver tube or are they different size and thread?

    1. That is answered in the article and in this very thread…

  12. I bought an mp 15 S&W carbine how do I Know if it is commercial or Mil spec??


  13. I really like the information I found please continue thank you

    1. When looking to get a new buffer tube I stick with mil-spec , there are more selections of stocks to choose from. I also get what manufacturers called enhanced buffer tubes . They have tabs at the bottom of the threaded end and a slot cut for the spring and buffer detent . These extended tabs cradle the bottom of the bcg . The bcg will be resting partially in the buffer tube which creates a smoother recoil action and eliminates BCG tilt .

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