Olympic is **** from everything I have read. Rock River is a decent contender. Colt invented it, and I own a model 6951. I cannot reccomened it enough. The 6951 is flawless. The magazine to use is the MetalForms mag. They are pricey, but so is your life. The MetalForms are the OEM supplier to Colt, the only difference is the marking on the floor plate. I have tried ASC, and ProMag, but again they are ****. I would particularly stay away from the Glock fed style lowers. The Glock mags are flawless, but the bolt system as well as feeding are rubbish, as well as the majority of the Glock lower suppliers lowers.