It has been a while since I have posted an animation. This one, author unknown, shows how the balanced gas operating system works in the AK-107 and AK-108 rifles.
( If the animation is not playing, try this link: click here)
Wikipedia explains how the system works:
The AK-107 and AK-108 represent a significant change to the Kalashnikov operating system originally designed in the late 1940s. The new rifle features a balanced system that functions along the lines of Newton’s third law of motion, which states that for every action there is an equal and opposite reaction. This system uses a recoil-dampening countermass mechanism with two operating rods that move in opposite directions, thereby providing “balance”. One operating rod, the upper, has a gas piston facing forward while the bolt carrier also has a gas piston. The gas tube at the forward end of the handguard is double-ended to accommodate the two rods. The enlarged gas tube cover of the upper handguard guides both rods in their travel.
When the rifle is fired, gas is tapped from the gas port to enter the gas tube, driving the bolt carrier to the rear and the counter-recoil upper rail forward. The critical timing of the reciprocating parts is accomplished by a star-shaped sprocket that links and synchronizes both components, causing both to reach their maximum extension, or null point where forces are exactly equal, at exactly the same instant. The felt recoil is therefore eliminated, enhancing accuracy and assisting control during fully automatic fire. The travel distance of the AK-107 reciprocating parts is less than other Kalashnikov designs, so the cyclic rate is higher at 850–900 rounds/min rather than 600 rounds/min on other AK rifles. However, as the felt recoil is virtually eliminated, the manufacturer claims that accuracy is enhanced, especially during burst fire. An enhancement of 1.5 to 2 times has been reported.
The system was previously used on the prototype AL-7 and AEK-971 rifles in the 1970s.
Hat Tip: fuliginosus @ guns.reddit.com