Buffer Tube Variations Explained

While all buffer tubes seem to look and function exactly the same, there a few variances and options available to the rifle builder. The buffer tube (AKA receiver extension tube), serves two purposes.

• 1)  It allows the user to attach a stock to the rifle
• 2)  It encapsulates the buffer and buffer spring, letting the bolt carrier ride back and forth to eject the spent brass and load the next round

Out of all the differences in buffer tubes available on the market, the two biggest differences are mil-spec and commercial spec tube sizes. While the primary differences between the two are the outside diameters, the below overviews help to explain why there are differences.

Mil-Spec Overview

What is Mil-Spec?  Military Specifications are standards put in place by the General Accountability Office (GAO) for defining requirements and standardized measurements of equipment used by the military. These standards have been established to guarantee interoperability, commonality and reliability for each part purchased for military use.  

As the name suggests, Mil-spec buffer tubes meet the requirements of the GAO. On the mil-spec buffer tube… the threads at the front are actually a larger diameter than the rest of the tube itself. In manufacturing, a large tube is used and threads lathed as normal. Next, the rest of the tube must be milled down to the military specified diameter. In summary, mil-spec tubes are a forged, one piece design and the threads are rolled. The outside diameter of a mil-spec tube is 1.148".

The following brands use the mil-spec diameter buffer tubes - LWRC International, LMT, HK, Colt, Smith & Wesson, Armalite and others, including all Strong-Side Tactical products. 

Commercial Spec Overview

For the commercial style tubes, the manufacturers begin with a tube that matches the final tube diameter. The threads are “cut” into the front end with a lathe just like any other threaded pipe. The end cap on commercial tubes are usually welded on, so in essence commercial tubes are really made from two pieces of material. The outside diameter of commercial spec tubes are 1.168".

The following brands use commercial diameter buffer tubes - Bushmaster, DPMS, Rock River Arms, YHM and others.

*Manufacturers can change parts on their rifles throughout the years, so please double check your diameter and confirm the back end shape before replacing a buffer tube so that it will fit your stock.

Real World Differences

Because pictures are worth a thousand words, the below diagram does a great job of explaining the dimensional differences…

So....Which One Do I Choose?

The million dollar question... is one better than the other? To keep it simple, no. However, some may argue that mil-spec buffer tubes are stronger based on the tensile strength of the aluminum used or the way that the tube is made. While this may be true, there are no case studies showing that commercial spec tubes are structurally inferior in any way, so we can't confirm.

While there are no functional differences between the two, we (Strong-Side Tactical) typically recommend using mil-spec buffer tubes for the simple reason that there are more options in the marketplace for stocks. While some of the larger stock manufacturers, such as Magpul, offer many of their products in both mil-spec and commercial, others like LMT only offer theirs in Mil-spec configuration. As with anything, you get what you pay for. Be wary of cheap buffer tubes, as the threads can crack and round over when the castle nut is tightened, throwing your stock off center. 

Additional features can be found on certain buffer tubes. LMT's Buffer Tube offers a fantastic option that has an extra leg to contact the retainer, locking it into place better than Mil-Spec. Some buffer tubes offer numbered stock locations to make it easier to find your length setting in a hurry. Internal coatings on some tubes provide a slick surface help to enhance the buffer action and make it smoother. V SEVEN's Buffer Tube is an outstanding buffer tube that has some different aesthetics and a great black finish. For those of you who are looking to place more weight to the rear of your rifle for a more balanced feel, V SEVEN also makes a heavy buffer tube to help move the weight bias to the rear. 

Variety is the spice of life, mil-spec tubes enable the rifle builder a much larger assortment of rifle stocks for their perfect rig. 

Rifle Buffer Tubes

Rifle buffer tubes are very basic when compared next to a carbine or pistol tube. The rifle tubes are longer and don't have a slot for an end plate, which are not used with rifle length, fixed stocks. The stock will secure the rear take down spring once it is installed. 

Pistol Buffer Tubes

When using a barrel shorter than 16", you must either have a registered lower receiver or a lower that has been converted to a pistol. Using a short barreled upper receiver on an unregistered lower receiver with a rifle stock is against the law. Since some people don't want to go through the hassle of registering with the ATF and paying the $200 tax, the next best option is to get a pistol lower receiver. 

A pistol buffer tube cannot accept a rifle stock and is concentric, but most will accept an arm brace. The arm brace was made popular by Sig Sauer and has been re-hashed by many other companies. This contraption was brought to market to help with disabled shooters who wanted to help support their arms while shooting AR pistols. The extra surface area and brace helps stabilize the rifle on your arm. 

*The ATF has recently reversed their previous opinion that the Sig type arm braces could be shouldered when fired. At this time, the ATF's opinion is that if you shoulder an arm brace, it is using the product for a purpose it was not intended for.