One question commonly asked by gun owners and buyers who have a specific interest in AR-15’s and AR-15 accessories relate to the rifle’s buffer tube. Specifically, they want to know which is better: the commercial spec version or the mil-spec one. For someone with sights set on upgrading the stock, or even assembling a new custom AR-15 from scratch, it is vital to understand the slight differences when it comes to buffer tube specifications.
The AR-15 Buffer Tube
The buffer tube of the AR-15 is also called the receiver extension tube; it is a metal protrusion from the body of the rifle which performs two distinct functions. Firstly it holds the mechanism of the recoil buffer, and second is that it forms the attachment point where the buttstock of the rifle is connected. The reason why they call it a “buffer tube” is that it has a large spring termed as the “action spring” on the inside, along with a weighted component called the “recoil buffer”.
Mil-spec vs. Commercial
When it comes to the difference in types, the first aspect to consider is the diameter of the part over which the stock slides on top of the tube. With mil-spec, the buffer tube is around 0.12 mm smaller than the commercial standard. While this may sound trivial, it does make an impact if you ever have the misfortune of mixing up buttstocks. Other than that, there are a few differences which many enthusiasts would be eager to point out, but none of the individual differences are guaranteed given that each can vary depending on the manufacturer you pick from.
Knowing the Right Buttstock Size
The buttstock is something you need to match with your rifle’s buffer tube before you pick any specific components. Most stocks these days come in both commercial and mil-spec types. You need a micrometer to take the right measurements and ensure their accuracy. When checking the diameter of the tube, something in the vicinity of 1.146” would mean you are holding mil-spec, while if the measurement lands somewhere about 1.17”, you can infer that the component is up to commercial specifications.
Why Not Just One Standard?
The answer to this is simple enough — money. Mil-spec designs were the original buffer tubes to be manufactured, but consequently someone had the idea of using a different manufacturing process made the gun components much cheaper. That’s why we have standard, economical, and widely accessible mass-manufactured AR-15 accessories and parts today. That is pretty much how commercial spec, high quality firearm accessories came into being.