Masterpiece Arms Defender 5.7x28mm The new 57DMG uses a fully machined aluminum lower receiver and fully machined aluminum grips. The coating on this model is cerakote black, but other colors are available. The machining of the lower and grip reduces weight and certainly increases the level of comfort and ergonomics from their previous design MPA57SST. Each receiver is laser engraved with the appropriate information. The new design also provides complete compatibility with the FN57 magazines in both 20 and 30 round capacity.