In the simplest terms, the Bushmaster Gas Piston System cycles the rifle’s action by using gas pressure to move a Piston and an Actuating Rod. This differs from the standard AR15/M16 Type rifle (with Gas Impingement System) wherein gas pressure is routed all the way back into the Upper Receiver to act directly upon the Gas Key, Carrier and Bolt.
The Bushmaster Gas Piston System Rifles and Uppers solve the common AR15/M16 Type rifle problems of excess heat buildup in the Receivers/Bolt Carrier, carbon build up, and gas leaks, by eliminating the need for Gas Tube and Gas Key of the standard system. Much like the operating systems found on AK-47 and FAL rifles, the Gas Piston System functions by tapping gas pressure off through a port in the barrel as the rifle is fired. Gas pressure pushes a Hard Chrome Plated tubular Piston (located within the Gas Block, just forward of the handguards), which drives a solid steel Operating Rod to the rear - into the Upper Receiver. There, the Operating Rod pushes a Striker Key on top of the Bolt Carrier to move the Carrier to the rear, and thereby cycles the rifle’s action. After initiating movement of the Operating Rod, excess gas pressure bleeds off through ports in the piston’s housing (the Gas Block) and exits within the Handguards to keep carbon build up and powder residue from reaching - and fouling - the interior of the Upper Receiver and Bolt Carrier.
This Bushmaster Gas Piston System operates at a lower cyclic rate, functions with a wider range of ammunition, and works with less gas pressure than the standard gas impingement system rifles to improve reliability and control, as well as reduce recoil, and heat in the receivers. The detented Gas Plug at the front of the Gas Block allows easy removal for maintenance and cleaning of the system’s Hard Chrome Plated Piston.
Both Complete Rifles and Barreled Upper Receiver Assemblies are available from Bushmaster. The Upper Receiver Assemblies will fit on, and work with, any military pattern 5.56mm/.223 caliber Lower Receiver. Gas Piston Uppers will function with all standard 5.56mm/.223 caliber magazines.