80 Percent Arms | Feb 17th 2021
What Are AR-15 Buffer Tubes?
Rifle buffer tubes are officially known as receiver extensions because there is a large spring inside the tube known as the buffer spring. The recoil buffer is the weighted part. Buffer tubes are an aluminum housing attached to the rifle's lower receiver, and they contain the AR15 buffer and the recoil spring. They also act as a mounting point for the buttstock or pistol brace.
There are different types of buffer tubes available on the market, and they both function well in firearms. You need to understand the difference between mil-spec and commercial buffer tubes to know which one is compatible with your gun. While the mil-spec and commercial buffer tubes have some similarities in look and performance, there are some key differences that will be important to consider when shopping for buffer tubes.
The Differences Between Commercial and Mil-Spec Buffer Tubes
The significant difference between the mil-spec and commercial AR-15 buffer tubes is the outer diameter of the stock-end, which will also determine the type of buttstock you buy.
At the buttstock end, the commercial buffer tube is .02” wider than the mil-specific buffer tube—1.168" vs. 1.148" diameter respectively. But at the receiver end, the mil-spec tube diameters are .015” wider than commercial spec tubes at 1.170” (including the height of the threads) vs commercial tubes which are 1.185".
The buffer tubes also differ in their manufacturing processes. The mil-spec tube threads—produced from 7075 T6 alloys—are rolled into the metal, resulting in taller and stronger threads. Commercial tube threads, on the other hand, are constructed from 6061 T6 billet aluminum and are cut into the metal, producing slightly shorter and weaker threads but at a lower cost. Other differences vary from manufacturers, including type of metal used and the angle of the back of the tube.
Should You Buy a Commercial or Mil-Spec Buffer Tube?
When it comes to the strength and capability between the types of tubes available, we can’t say that one supersedes the other. But still, we recommend you use a true mil-spec tube, if only because it has become the standard type of tube for AR-15 rifles.
For this reason, mil-spec buffer tubes are more widely produced and compatible with many different AR-15 parts. Your average retailer or gunsmith will produce parts with mil-spec configurations so that they are able to sell buffers, buttstocks, and the like to law enforcement agencies, who use mil-spec rifles. So, although mil-spec buffer tubes might cost more than commercial style tubes, you’ll have an easier time finding them and they’ll be more likely to fit your build.
Can Commercial Tubes Work With Mil-Spec Buttstocks and Lowers?
Sadly, no. The issue with commercial and mil-spec tube compatibility lies in the difference in tube size, which we covered earlier. Because the discrepancy is so small, there’s no way to retro-fit one to the other either, and attempting to force a fit will either cause destabilization or even damage to the components.
The slight differences in thread height will also cause issues if you try to fit a commercial tube on a mil-spec lower receiver and vice versa.
You also will be hard pressed to secure a mil-spec buffer tube to yourlower receiver using a commercial castle nut and end plate.
A Few Exceptions
While the outer dimensions might affect mil-spec and commercial tube compatibility with some parts, they have essentially identical insides. That’s right—you can choose just about any bolt carrier group, buffer, or spring for your AR-15 configuration because those dimension differences won’t negatively impact BCG and cycling round functionality.
