There are many magazines available for the AR-15 family of firearms and various weapons that are capable of accepting the STANAG magazines. Which ones do you choose? Based on 25+ plus years of using this weapon system and a decade on SWAT to present, I have found that certain brands perform to my expectation. This video is about the brands and manufacturers of magazines that I recommend.
Some sites stocked with good magazines: Rainierarms.com , dsgarms.com , sgammo.com , aimsurplus.com , 44mag.com , specializedarmament.com , operationparts.com , botach.com , bravocompanyusa.com , gandrtactical.com
A STANAG magazine or NATO magazine is a type of detachable firearm magazine proposed by NATO in October 1980.
Wikipedia:
A STANAG magazine[1][2] or NATO magazine is a type of detachable firearm magazine proposed by NATO in October 1980.[3] 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 magazine was 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".[4]
The STANAG magazine, while relatively compact compared to other types of 5.56×45mm NATO box magazines, has often been criticized for a perceived lack of durability and a tendency to malfunction unless treated with a level of care that often cannot be afforded under combat conditions. Because STANAG 4179 is only a dimensional standard, production quality from manufacturer to manufacturer is not uniform. Magazines have been manufactured with lightweight aluminum or plastic bodies and other inexpensive materials in order to keep costs down, or to meet requirements that treat the magazine more as a disposable piece of equipment than one that is supposed to stand up to repeated combat use.
As a result, in March 2009, the U.S. military began to accept delivery of improved STANAG magazines.[10] To increase reliability, these magazines incorporate heavier, more corrosion resistant springs and new tan-colored anti-tilt followers.[11] In addition, many commercial magazine manufacturers now offer improved STANAG-compatible magazines. These magazines are made from high-grade stainless steel bodies, rust- and set-resistant chrome-silicon springs, and anti-tilt followers. There are also highly reliable polymer magazines, some with view windows, others are translucent.