Our M-16 / AR-15 Modular Buttstock Magazine Pouch (BMP) holds 1 spare 30 round magazine on the offside of the buttstock. Secure, but readily accessible, this gives the shooter a spare magazine that's always with the weapon. A highly valuable feature of this BMP is that it is modular, completely ambidextrous and can be easily attached to the rear adapter of any of our fixed stock M-16 / AR-15 tactical slings. NOTE: This item is a stand alone unit and is supplied with a rear adapter in addition to the front strap. The intent of this particular BMP variant is for users who want a BMP but are running a 1 point sling or standard carry strap that doesn't use, or require, a rear sling adapter. If your are purchasing a BMP to be used with a Specter Gear fixed stock 2 point or 3 point M-16 / AR-15 tactical sling that you are purchasing now, or already own, you will be provided with the proper rear adapter to interface with this BMP. So, we would suggest you purchase the BMP kit, which is not supplied with a rear adapter instead of this one. This will save you money and you won't end up with an extra rear adapter you don't need.