A compact action for a firearm including an upper receiver housing incorporating a barrel. A bolt and supporting carrier is positioned within the receiver housing so that the bolt is engaged to a rear receiver end of the barrel in a cartridge chambering position. Guide rods are supported within the housing above the barrel and extend in parallel to a rear located end plate. The carrier includes a carrier key supported by and displaceable along the guide rods between the barrel and a rearward bumper component. A gas tube extends from a forward located gas block overlaying a gas discharge aperture in the barrel to a gas key for actuating the carrier rearwardly following discharge of a ballistic from the barrel. A charging handle is manually displaceable along a slot in the housing for actuating an interior slider component, in turn actuating the carrier key to cycle the carrier and bolt.