Mil-Spec vs Commercial Spec Buffer Tubes: What’s the Difference?
If you’ve ever shopped for AR-15 parts or built your own rifle, you’ve probably come across the terms mil-spec and commercial spec buffer tubes. These two types of buffer tubes look similar at a glance, but there are important differences that can affect compatibility with stocks and overall fitment. Understanding these distinctions will help you choose the right parts for your build and avoid frustrating fit issues.
What Is a Buffer Tube?
The buffer tube (also called a receiver extension) is the cylindrical part attached to the lower receiver of an AR-15 style rifle that houses the buffer and buffer spring. It also serves as the mounting point for the rifle’s stock.
Buffer tubes come in two main standards: mil-spec (military specification) and commercial spec (civilian or commercial specification).
Why Does Diameter Matter?
The biggest physical difference is the diameter of the tube. Mil-spec tubes are slightly smaller in diameter than commercial tubes. This matters because the stock’s buffer tube clamp or sleeve must fit snugly around the buffer tube.
-
If you try to put a commercial spec stock on a mil-spec buffer tube, the stock will be loose and may wobble.
-
Conversely, a mil-spec stock won’t fit over a commercial spec buffer tube because the tube is slightly larger and won’t slide inside the stock.
How to Tell Them Apart?
-
Measure the diameter: Use calipers to measure the outside diameter of the buffer tube near the receiver end.
-
Check the product description: Most manufacturers clearly specify whether a buffer tube or stock is mil-spec or commercial spec.
-
Fit test: Stocks often have a marking or product listing to indicate which buffer tube type they are designed for.
What About Length and Weight?
The length difference is minimal but worth noting if you are working with very precise setups. Mil-spec tubes tend to be slightly longer and lighter due to thinner walls.
Which Should You Choose?
-
If you want a military-style rifle or parts compatibility, go with mil-spec buffer tube and mil-spec stocks.
-
If you’re buying aftermarket stocks designed for commercial buffer tubes, such as many collapsible stocks from companies like KIRO or IMI Defense, choose commercial spec tubes.
-
Be consistent: match the buffer tube and stock type for a secure, wobble-free fit.
Final Tip
Always check your stock and buffer tube specs before purchasing parts. Using the wrong combination can result in a loose or unusable stock and may require replacing or modifying components. When in doubt, ask your parts supplier or consult manufacturer specifications.
