Slop in fitting the barrel extension to the upper receiver can rob your rifle of its potential accuracy.
by Joe Carlos
photos by Gretchen Huffman
Stoner platform guns don’t assemble the same way as most other rifles. Take bolt guns for example. In M24 sniper rifles the front of the receiver has a female thread machined into it and the back of the barrel has a corresponding male thread and the barrel physically screws into place during assembly of the rifle. Contrast this to the M16. The barrel extension is not integral with the barrel. It is not a part of the barrel. It is a cylindrical piece of metal about 1 1/8” long machined separately. At one end of the barrel extension there is a raised collar, often called a flange, all around its circumference which abuts against the front of the upper receiver when everything is assembled and in place. The barrel is threaded at the rear (much like a bolt gun barrel) and it physically screws into a female thread in the barrel extension. That barrel extension simply slips into the front of the receiver upon assembly – it is not directly threaded into the receiver in any way.
Since it is a slip fit there is a lot of play. Anyone who has ever rebarreled or watched someone assemble an AR-15 upper will note that up until screwing the barrel nut in place the barrel will wiggle around, giving a lot of potential accuracy robbing slop.
Read more in our March 2013 issue. Back issues are available.