Maximum firepower for your Ruger 10/22! Sturdy 55 Round magazine is made of rugged polymer. Fits most 10/22 models, .22LR and .17 Mach 2. Only the finest polymers go into ProMag magazine bodies. The springs are precision wound using heat treated chrome silicon wire. Followers are injection molded from polymers selected for their durability. Each and every ProMag is made right here in the U.S.A.