The Phase 5 Carbine Mini Stock Assembly (CMSA) is a combo kit featuring Phase5's Universal Mini Stock (UMS) and HexOne buffer tube for an excellent compact fixed stock solution. The UMS is also compatible with a number of other buffer tubes, including Mil-spec carbine receiver extensions and most round tubes, it was designed to complement the sturdy HexOne buffer tube. The UMS and HexOne are precision machined in house from USA sourced raw billet aluminum. The HexOne buffer tube is cut from 7075-T7 and the UMS is 6061-T6. The buffer tube features a hexagonal design that is much thicker and rugged than a mil-spec receiver extension tube making it perfect for 5.56 NATO, 300 BLK, or even calibers like 7.62x39 and .308. It will also work with pistol caliber carbines such as 9mm, 40 S&W, and 45 ACP, but you may need a different buffer and/or spring. The UMS offers a smaller footprint and bottom curve which makes for a far superior anchor of the stock on the chest. This allows an operator to get in and out of position with greater of ease.