Mil-Spec VS Commercial Buffer Tubes

AR-15 adjustable buffer tubes (correctly known as ‘receiver extensions’) come in two different sizes. It is important to know which tube you have as this impacts your selection of a buttstock. A mil-spec stock will fit on a commercial tube, but will be wobbly, however a commercial stock will not fit a mil-spec tube at all. Knowing your parts allows you to make the correct choice.

Check out this picture and look at the differences in tubes.

MilSpec_vs_Commercial Extension

You will first notice the mil-spec tube is slightly larger in diameter. When looking at tubes without a micrometer, it is easier to see that the commercial tube is slanted 5* at the rear when viewed from the size, while a mil-spec tube rear is straight and perpendicular to the side. The other minor difference and perhaps the most important for strength are the threads. On a mil-spec tube the threads are cut correct with full engagement where a commercial tube has extruded threads that are rounded off instead of having sharp peaks.

If your part was a cheaper tube or in a kit chances are it’s a commercial tube. There’s no *huge* difference between tubes except size, so don’t sweat it unless you are butt-stroking tangos often or breaching doors. Me, I want what is closest to what the military is using so I pay the extra couple bucks and go with a mil-spec tube for the piece of mind.