AR15 Rifle Stocks

Do I need a Commercial or Mil-Spec stock for my AR15 Carbine Rifle?

A common question when purchasing a new stock for your AR rifle is, does it require a Commercial or Mil-Spec stock? To determine this you need to know what kind of buffer tube you have installed. The difference between a Mil-Spec and/or Commercial tube is size, both the tube diameter and the threads. The Commercial tube is slightly larger measuring ~1.170" and has threads which appear flat, consistent with the diameter of the tube. The Mil-Spec tube diameter is ~1.145", (~1.185" at threads) and has threads that have well-formed peaks and measure greater than tube diameter. As a general rule the following AR rifles require a "Mil-Spec" stock; Colt, Bravo Company, Daniel Defense, LMT, Smith & Wesson, Stag Arms, CMMG, Ruger, LWRC, Spikes Tactical, Vltor, & Armalite (Current Production). The following AR rifles use a commercial stock; Sabre, Bushmaster, Rock River, DPMS, Olympic Arms & Armalite (Older Production).

A Commercial stock will typically fit on a Mil-Spec tube, but will be loose and rattle. Mil-Spec stocks will not fit on a Commercial tube.

AR15 Commercial Buffer Tube Measurement AR15 Milspec Buffer Tube Measurement
Commercial Buffer Tube MilSpec Buffer Tube

I currently own an A1/A2 Rifle and want to add an adjustable Carbine stock, what will I need?

The A1/A2 Rifle Buffer tubes are all produced to mil-spec standards. Both the A1/A2 tubes are the same diameter and length, however the A2 tube adds a 5/8" spacer to the standard A1 tube. This additional length is to accommodate the redesigned stock on the A2 model rifles. Enough of that, getting back to the question of what is required to add an adjustable Carbine stock to your A1/A2 rifle. To accomplish this you'll need to change out the tube, buffer, and spring. Do not attempt to use an A1/A2 buffer and/or spring with a carbine length tube, they are not interchangeable. The rifle buffer is much longer and will create a dangerous, possibly deadly situation. The easiest way to ensure you have the correct parts is to use a kit available from ATI. The ATI kit includes all of the parts you'll need to convert your A1/A2 to an adjustable Carbine style rifle.


Looking for additional help, checkout this video provided by Tapco. It gives step by step instruction on installing a carbine buffer tube, buffer, and spring on your A1/A2 rifle.