Check this placard from Agilite Gear designed to hold multi-calibre magazines... "The Pincer Placard Multi-Caliber is a hook-backed elastic plate carrier placard that holds three 5.56/7.62x39/PCC magazines or six 9mm extended Glock Mags. Its revolutionary Patent Pending funneled magwell design allows you to grab or re-index a magazine with just one hand while still maintaining rock solid retention so your mags never fall out."