The AMAG 21 SG9 is a 21-round SIG P320 9mm handgun magazine featuring a stainless-steel body with polymer sub-components. Magpul AMAGs come with many of our standard proven features, including a high-visibility, controlled-tilt follower, stainless-steel spring, flared floorplate that's easily removable for cleaning and routine maintenance, paint-pen dot matrix for magazine marking, and capacity-indicator windows which begin at five (5) rounds, and continue along the spine of the magazine in one (1)-round increments.