Gas-operated reloading is a system where energy is used to operate autoloading firearms. A portion of high-pressure gas created from explosive propellant is used to power the mechanics, extract the spent casing, and chamber a new cartridge. Energy from these high-pressure gasses are harnessed through a gas port along the barrel. This gas impinges on a surface such as a piston head or through a tube to provide motion for the unlocking, extraction of spent case, ejection, cocking of the hammer or striker, chambering of the new cartridge, and locking of the action.
Direct Impingement System
The Direct Impingement (DI) method of operation vents gas through a tube into the working parts of the rifle where they directly impinge (has an effect on) the bolt carrier.
Advantages - 1. Has the absolute minimum amount of recoil on the rifles action and parts (for auto & semi-automatic weapons), resulting in the minimum possible weapon disturbance caused by balance shifting during the action cycle, potentially improving accuracy 2. Reduces overall weapon weight 3. Direct impingement guns are more suppressor friendly, especially those with an adjustable gas block that allows you to control the amount of gas directed back through the gas tube. 4. Spare parts for these gas systems in AR style rifles are plentiful, easy to find, and cheap.
Disadvantages - 1. Propellant gasses and their accompanying fouling are blown directly into the action parts making them very dirty. As a result, high maintenance and regular cleaning is absolutely necessary. 2. DI operation also increases the amount of heat that is deposited in the receiver while firing, which can burn off essential lubricants. Lack of lubrication is one of the most common causes of weapon stoppages and jams. 3. The bolt, extractor, ejector, pins, and springs are also heated by this high temperature gas, which causes increased wear and tear and reduces the service life of these parts and the weapons reliability.
Gas Tube. See the M16
Long-Stroke Piston
With a long-stroke system, the piston is mechanically fixed to the bolt group, and moves through the entire operating cycles as one with the bolt group.
Advantages - 1. Design simplicity and robustness. 2. The mass of the piston rod adds to the momentum of the bolt carrier enabling more positive extraction, ejection, chambering, and locking. 3. The gas is not directed back into the chamber, keeping the weapon cleaner for much longer and reducing the chances of a malfunction.
Disadvantages - 1. Disruption to the point of aim caused by the centre of mass changing during the action cycle, and by energetic and sudden stops at the beginning and end of the bolt carrier travel/reload sequence. This may make piston driven rifles less accurate. 3. More gas is required to operate the system due to the greater mass of moving parts.
Piston rod is attached to the bolt carrier. See the Ak-47, FN MAG
Short-Stroke Piston
With a short-stroke or tapped system, the piston moves separately from the bolt group. It may directly push the bolt group parts (M1 Carbine), or or it may operate through a connecting rod or assembly (Armalite AR-18). In either case, the energy is passed in a short, violent push and the motion of the gas piston is then engaged allowing the bolt carrier assembly to continue through the operating cycle through kinetic energy.
Advantages - 1. This system reduces the total weight of recoiling parts compared to the long-stroke piston. This allows for better control of the weapon (compared to long-stroke piston) due to less mass needing to be stopped at either end of the bolt carrier travel. 2. The weapon system stays cleaner longer and therefore reduces the chances of a malfunction, when compared to the DI gas system.
Disadvantages - 1. There may be a small disruption to the point of aim due to the centre of mass changing during the action cycle. 2. Slightly more recoil may be felt when compared to the gas impingement system. 3. Good quality short-stroke piston rifles are expensive.
Piston Rod. See the SA80
Article References: https://en.wikipedia.org/wiki/Gas-operated_reloading
