Experience unparalleled durability with the ProMag Industries SMI21 magazine, expertly engineered in the USA for optimal performance. Crafted with precision, this magazine features a heat-treated chrome silicon spring, ensuring reliability and longevity. Rigorous quality control during assembly guarantees every magazine meets the highest standards. Heat-Treated Chrome Silicon Wire Spring Manufactured & Assembled in the U.S.A. Easy Loading Rugged Construction Invest in the ProMag SMI21 for a dependable, high-performance magazine built to last a lifetime.