LMG Tactical's FMS Pouchis a pouch with a flap that tensions the magazine with an elastic rubber bungee cord.
 
FMS Pouch can up to two AR-15 magazines can be stored in the pouch, and the pouch tensions the rubber bungee cord.

Flap has a position adjust function, so it can hold up to 40 round AR-15 magazines.

Back side is laser cut slot molle attach system.