Abstract: A compact action for a firearm including an upper receiver housing incorporating a barrel. A bolt and carrier are 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 fixed ejector is attached to the upper receiver, in combination with machining a slot into the carrier and the bolt, such that the ejector remains static such that, upon the bolt cycling, the spent shell casing contacts the ejector, causing it to be ejected out of the upper receiver.