The maximum capacity for this magazine is (13) rounds. Will only hold .40 Smith & Wesson, and .357 Sig Sauer caliber rounds. Constructed of blued steel to achieve a long life, and also to avoid corrosion and wear in the long run. The hi-tensile compression spring will assure the magazine and your chamber continue to have great transitions, with no friction. This magazine also comes with a polymer base-pad, for supportive shooting.