This black oxide alloy steel 10-round 5.7x28mm Genuine Ruger Factory Magazine is compatible with the Ruger-57 Pistol. Factory replacement parts are manufactured to the exact same specifications and tolerances and use the same manufacturing materials as the original parts which guarantees excellent fit and reliable operation. Keeping a few extra factory magazines around is never a bad idea; extra magazines save loading time at the range and also serve as a backup for those days when you simply cannot remember where you put your primary magazine.