15 & 20 round magazines

A STANAG magazine or NATO magazine is a type of detachable firearm magazine proposed by NATO in October 1980. Shortly after NATO's acceptance of the 5.56×45mm NATO rifle cartridge, Draft Standardization Agreement (STANAG) 4179 was proposed in order to allow NATO members to easily share rifle ammunition and magazines down to the individual soldier level. The U.S. M16 rifle's magazine proportions were proposed for standardization. Many NATO members, but not all, subsequently developed or purchased rifles with the ability to accept this type of magazine. However, the standard was never ratified and remains a "Draft STANAG".

View More On Wikipedia.org