When it comes to purchasing an aftermarket rifle stock to upgrade your existing AR15s or to build a brand new one from scratch, it's important to be aware of the differences between mil-spec and commercial buffer tubes.
This article will delve into the specifications and reasons why a particular stock may not fit your AR-15's buffer tube.
Mil-Spec Buffer Tubes: Designed for Military Standards
Mil-spec buffer tubes are specifically manufactured to meet the stringent requirements and standardized measurements set by the General Accountability Office (GAO) for military use. These specifications ensure interoperability, commonality, and reliability of equipment used by the military.
Diameter and Length: A mil-spec buffer tube typically has a cross-section diameter of 1.14" and a length of 7.25". It is constructed from 7075-T6 alloy, which provides superior strength. The threading on mil-spec tubes is 1-3/16" x 16 TPI (threads per inch).
Design Features: Mil-spec buffer tubes have a flat end and are slightly shorter than their commercial counterparts. The construction materials and threading of mil-spec buffer tubes make them highly durable and resistant to wear and tear.
Commercial Buffer Tubes: Versatility and Cost-Effectiveness
Commercial buffer tubes, on the other hand, are designed with greater versatility and cost-effectiveness in mind. These tubes are often cheaper to manufacture compared to mil-spec tubes.
Diameter and Length: A commercial buffer tube typically has a slightly larger cross-section diameter of 1.17" (accounting for thread height) and a length of 7.25". Commercial tubes are often extruded rather than machined, resulting in a welded-on cap made from a less expensive metal.
Design Features: One noticeable visual difference is the slanted back of the commercial tube, which distinguishes it from the flat-backed mil-spec tube. Despite the differences in materials and manufacturing techniques, commercial buffer tubes function just as effectively as mil-spec tubes.
In terms of functionality, there is no significant difference between mil-spec and commercial buffer tubes. The buffer spring works identically in both systems, and even slight variations in dimensions do not affect performance.
While some mil-spec buffer tubes may have greater tensile strength due to the higher-grade aluminum used, there are no reliable case studies suggesting that commercial-spec tubes are structurally inferior. It ultimately comes down to personal preference and product availability at the time of purchase.
Compatibility and AR-15 Stock Fitment
Mil-Spec Stock Compatibility: Mil-spec stocks are designed to fit exclusively on mil-spec buffer tubes. The precise dimensions and threading of both the stock and buffer tube ensure a tight and secure fit, minimizing stock wobble.
If you have a mil-spec buffer tube, you must choose a mil-spec stock for proper compatibility.
Commercial Stock Compatibility: Commercial stocks, on the other hand, can fit on both commercial and mil-spec buffer tubes. This versatility allows users with either type of buffer tube to select from a wider range of stock options.
However, it's important to note that a commercial stock installed on a mil-spec buffer tube may result in a slightly looser fit.
The Castle Nut Thread
Regardless of whether you have a mil-spec or commercial buffer tube, the castle nut thread remains the same. All AR-15 receiver tubes are threaded with a 1-3/16" x 16 TPI castle nut thread.
This standardized threading ensures compatibility between buffer tubes and castle nuts, regardless of marketing labels used by different companies.