The ProMag Industries SMI 31 Magazines deliver unmatched reliability and performance, crafted meticulously for firearm enthusiasts. Manufactured in the USA, these magazines come with a lifetime guarantee against defects, ensuring your investment is protected. Utilizing heat-treated chrome silicon wire for the springs enhances durability and function, while stringent quality checks guarantee consistency. Heat-Treated Chrome Silicon Wire Spring Manufactured & Assembled in the U.S.A. Easy Loading Rugged Construction Choose ProMag for superior quality and peace of mind in every shot.