Complex sentence: The CPX uses an aluminum receiver inside the polymer grip housing or frame held on with steel pins, with a stainless steel barrel and slide (Carbon Black or Two-Tone Stainless), which lock open when the last round is fired.
Split into simpler sentences: The CPX uses an aluminum receiver inside the polymer grip housing or frame held on with steel pins. It has a polymer grip housing or frame with a stainless steel barrel and slide (Carbon Black or Two-Tone Stainless), which lock open when the last round is fired.