Complex sentence: The AR57 PDW Upper is a new design on an AR15/M16 platform, blending the AR15/M16 lower with a light weight, monolithic upper receiver system chambered in 5.7x28mm.
Split into simpler sentences: The AR57 PDW Upper is a new design on an AR15/M16 platform. Blending the AR15/M16 lower with a light weight, monolithic upper receiver system chambered in 5.7X28mm.