Why Gas Piston?

Why go gas-piston?

• Virtually eliminates fouling
• Imagine 13 times increased reliability
• Imagine 13 times the number of rounds between cleanings
• Imagine using your existing gun platform…….all of it except your gas tube.
• Machined out of the finest materials including Cobalt, which is 3X stronger than titanium!
• Fire your gun filthy…..covered in sand, mud, water and snow.
• Self Cleaning, actually removes its own contaminants.
• No venting means no holes for dirt and contaminants to enter the system.

Gas-operation is a system of operation used to provide energy to operate autoloading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed through either a port in the barrel or trap at the muzzle. This high-pressure gas impinges on a surface such as a piston head to provide motion for unlocking of the action, extraction of the spent case, ejection, cocking of the hammer or striker, chambering of a fresh cartridge, and locking of the action. This gas entering the action of the firearm brings with it heat, dirt, and contaminants which can cause function to fail over time.

History of development

The earliest self powered automatic firearms, such as the Maxim gun, were based on using the power of recoil to operate the mechanism. While this was effective, it led to problems due to the complexity imposed by the requirement that the barrel slide rearward a short distance in recoil. In 1891, John Moses Browning, a well known designer of lever action firearms, filed his first patent for an automatic firearm that harnessed expanding propellant gas to operate the mechanism. The prototype gun, built in 1889, used a baffle at the muzzle that deflected the escaping gas of the muzzle blast, and used that energy to cycle the action of a .44 caliber rifle, allowing it to fire 16 shots in under one second.

In 1892 Browning licensed the patent to Colt, and by 1895, the design had been refined to produce the M1895 Colt-Browning machine gun. The baffle had become a piston near the middle of the underside of the barrel. The cylinder connected to a small port in the barrel that forced a piston, attached to a hinged arm, down and rearward. This energy was used to cycle the belt feed mechanism of the machine gun. While the swinging arm below the barrel was awkward (resulting in the nickname “potato digger” after its tendency to dig into the ground if fired from too low a position) it was adopted by a number of militaries around the world in calibers ranging from 6 mm Lee Navy to .30-40 Krag and .30-06 Springfield. The M1895 was exported to Russia in 1914 for use in World War I and saw service in England, France, and various countries in South America.

A later variant of the M1895, commonly called the Marlin Gun after its builder, Marlin-Rockwell (now Marlin Firearms), replaced the swinging arm with a long cylinder and a piston attached directly to a the rod that operated the action. This version was designed for use on tanks and aircraft, and it remained in production through the end of World War I. The Marlin Gun’s long cylinder design would later be used by Browning in the design of the M1918 Browning Automatic Rifle, and by John C. Garand in the final version of the M1 Garand.[2]

Other builders began experimenting with gas operation soon after Browning. The French Manufacture d’armes de Saint-Étienne, or MAS, began experimenting with a new form in 1901 that eventually saw service as the MAS-49 rifle, and was copied by others, such as the Swedish Ag m/42. These rifles used a gas port located partway down the barrel, which is in turn connected to a tube that runs back to the bolt. This piston fits into a cylinder on the bolt carrier. While this uses the same short cylinder as the M1895, by applying the gas directly to the bolt carrier, the mass of the reciprocating parts is reduced significantly.

In 1931 inventor David Marshall Williams submitted a patent appliation for an automatic firearm which used a piston separate from, but acting on, the operating rod. This principle was used in the M1 carbine and variants. In 1956, Eugene Stoner patented a design that used a gas tube, similar to the MAS design, but rather than acting on the bolt carrier itself, it acted on a piston contained inside the bolt carrier. In this case, the bolt acts as a fixed piston, and the bolt carrier as a movable cylinder. Gas is routed into the bolt carrier, where it pushes upon the locked bolt, and in response the bolt carrier is pushed to the rear. This unlocks the bolt, disconnects the gas tube from the carrier, and the bolt and carrier continue travel rearwards to cycle the action. A rifle using Stoner’s operating mechanism was eventually adopted by the US military as the M-16 rifle.

Gas systems

Most current gas systems employ some type of piston. The face of the piston is acted upon by gas from the combustion of the propellant from the barrel of the firearm. Early methods such as Browning’s ‘flapper’ prototype, the Bang rifle, and Garand rifle used relatively low-pressure gas from at or near the muzzle. This, combined with more massive operating parts, reduced the strain on the mechanism. To simplify and lighten the firearm, gas from nearer the chamber needed to be used. This gas is of extremely high pressure and has sufficient force to destroy a firearm unless it is regulated somehow. Several methods are employed to regulate the energy. The M1 Carbine incorporates a very short piston, or “tappet”, that moves only a fraction of an inch prior to stopping against a shoulder recess. Excess gas is then vented back into the bore. The M14 rifle and M60 GPMG use the White expansion and cutoff system to stop (cut off) gas from entering the cylinder once the piston has traveled a short distance. Most systems, however, vent excess gas into the atmosphere through slots, holes, or ports.

Short-stroke piston

With a short-stroke or tappet system, the piston moves separate from the bolt group. It may directly push the bolt group parts as in the M1 Carbine or operate through a connecting rod or assembly as in the Armalite AR-18. In either case, the energy is imparted in a short, violent push and the motion of the gas piston is then arrested allowing the bolt carrier assembly to continue through the operating cycle through kinetic energy. This has the advantage of reducing the total mass of recoiling parts. This, in turn, enables better control of the weapon due to less mass needing to be stopped at either end of the bolt carrier travel. These sudden stops on other systems disrupt the weapon’s point of aim, especially with light weapons in full-automatic fire. The primary disadvantage of this system is that it relies more heavily on spring pressure and less on bolt mass for the kinetic energy to chamber a round and lock the breech.

Long-stroke piston

With a long-stroke system, the piston is mechanically fixed to the bolt group and moves through the entire operating cycle. This system is used in weapons such as the Bren light machine gun, AK47, and M1 Garand. The primary advantage of the long-stroke system, beyond design simplicity and robustness, is that the mass of the piston rod adds to the momentum of the bolt carrier enabling more positive extraction, ejection, chambering, and locking. The primary disadvantage to this system is the disruption of the point of aim due to the center of balance changing during the action cycle and energetic and abrupt stops at the beginning and end of bolt carrier travel.

Gas trap

A gas trap system is similar to long-stroke operation, however gas is ‘trapped’ after leaving the muzzle. The Bang rifle, early ‘gas-trap Garand’, and Gewehr 41 operated this way. These systems are longer, heavier, and more complex; however, they do use lower pressure gas and do not require that a hole be drilled in the barrel, two advantages that are largely negated by their disadvantages.

Direct impingement

The direct impingement method of operation vents gas through a tube to the working parts of a rifle where they directly impinge on the bolt carrier. Rifles that use this system include the M16 and French MAS-49. This system has the advantage of having the absolute minimum of recoiling action parts, resulting the minimum possible weapon disturbance due to balance shifting during the action cycle. It has the disadvantage of the propellant gas (and the accompanying fouling) being blown directly into the action parts.  A further disadvantage is that the bolt, extractor, ejector, pins, and springs are heated by this high-temperature gas. This heat dries out lubrication and changes the temper of the metal resulting in reduced life of these parts and shortening time between failures. .