SPS magazines have long been recognized by champion shooters around the globe as one of the best competition magazines. They were designed to be used in sporting pistols allowing high cap ammo. These magazines are legal for use in all USPSA competitions. These double stack mags have heat-treated 420 stainless steel bodies for added anti-corrosive capabilities while increasing the overall strength of the magazine tube. Polishing, both inside and outside of the magazine tubes, allows for perfect insertion into the magazine well, and extremely easy and smooth loading. The magazine springs are made of high quality heat-treated steel so that feeding and performance exceeds expectations. The removable base plate and follower are constructed of a durable polymer that prevents chipping and cracking. This mag locks the slide back when empty. These magazines are compatible with STI pistols.