Comparison of Mil-Spec and Commercial AR-15 Collapsible Stocks

Mil-Spec Stock Characteristics

Mil-Spec Stock Characteristics

A Mil-spec stock is required when you have a mil-spec buffer tube. The buffer tube is also called the lower receiver extender. Mil-spec tubes are smaller in diameter and have threads that are larger than the actual tube. The mil-spec tube is ~1.48″ in diameter. Mil-spec tubes also tend to have stronger threads which leads to a better overall gun setup. The tube is made from 7075-T6 alloy which creates 1-3 and 16-16 UN thread rolls. When being manufactured, the threads are first lathed as normal, then the tube is milled down to the military specific standards.

Commercial AR-15 Collapsible Stocks Characteristics

Commercial Stock Characteristics

A commercial collapsible stock will fit on a buffer tube that is ~1.168″. They were created as a cheaper version to reduce costs to those wanting to have a more cost effective setup. They cost less because the extension is manufactured from an extruded tube and the tube has a welded on cap that’s usually made from a lesser metal. The threads match the 1-3 and 16-16 threads of the mil-spec but may not be as durable. The commercial stocks are often slanted at the point of attachment.


The differences between the mil-spec collapsible AR15 stock and the commercial collapsible stock are small but very important. The stocks can look almost identical but key differences will determine whether or not you have a successful setup. When deciding between a mil-spec and commercial collapsible stock its important to note that the buffer tube size is the most important consideration.

Mil-Spec vs Commercial AR-15 Collapsible Stocks

These stocks are not interchangeable so tube size must be considered. If you wish to switch from either mil-spec to commercial or vice versa you can change out the buffer, tube and spring. Mil-spec stocks will often give you more options as far as the type of stock you want. They just tend to be more common and you can find a wide variety of collapsible mil-spec stocks. Also it’s usually found that with mil-spec stocks, the fitting may be more consistent over different brands.

It’s not always true but the following brands normally will use a mil-spec stock: Colt, Bravo, Daniel Defense, Smith & Wesson, Ruger and Spikes Tactical. Sabre, Bushmaster, Rock River, DPMS, and Olympic Arms usually will require a commercial collapsible stock. A commercial AR stock will go on a mil-spec tube but won’t fit exactly as it should and may leave some play at the connection, whereas a mil-spec stock will not fit on a commercial tube at all. Commercial stocks tend to be slanted at the attachment point where mil-spec stocks will be straight. Milspec stock tend to cost more than commercial stocks because they are costlier to manufacture but you often get a return on your investment based on the higher quality of the mil-spec stocks.