Bringing together a number of patented Leitner-Wise technologies in one performance package, the BOOMBOX complete upper receiver is a reimagined concept that marries the early 604 receiver style with modern, state-of-the-art, internals. The heart of this includes the Long Advance Carrier with corrected cam path; Combat Match Bolt; Precision Cam Pin, and Titanium Firing Pin. A Cold Hammer Forged 41V45 CMV Steel 16" Combat Match Barrel, 1 in 7 right-hand six groove twist, with Nitrided finish.

Powering the system is the patented Leitner-Wise non-adjustable short-stroke piston operating system. This utilizes a one-piece, fluted, and fully supported operating rod, with true self-regulation for over-pressure. A quick-detachable gas block, for disassembly if required. All heat, pressure and friction surfaces are nitrided then hard chrome plated for durability and adverse environmental condition capability. The operating system is tuned and timed correctly allowing the use of a carbine buffer and spring which minimizes reciprocating mass for smoother operation.

The BOOMBOX 604 Upper Receiver is forged from 7075 aluminum with the period correct "carry handle", no shell case deflector, polymer ejection port cover, and M4 feed ramps. The 12.6" handguard is machined from aircraft grade, heat-treated, extruded aluminum and designed to provide optimum cooling and airflow for the barrel, light weight, and high strength. A ambidextrous Raptor LT charging handle is utilized and all BOOMBOX uppers are supplied with installed period correct rear sight, lightweight aluminum A frame removable front sight, BOOMBOX carbine buffer and spring, and a Leitner-Wise Heavy Duty Buffer Retainer.