the Soviet Union during the late 1940s. The AK-47 uses a long-stroke gas system generally associated with high reliability in adverse conditions. The large gas piston, generous clearance between moving parts, and tapered cartridge case design allow the gun to endure large amounts of foreign matter and fouling without failing to cycle. Cartridge The AK fires the 7.62×39mm cartridge with a muzzle velocity of . The cartridge weight is , the projectile weight is . The original Soviet M43 bullets are 123 grain boat-tail bullets with a copper-plated steel jacket, a large steel core, and some lead between the core and the jacket. The AK has excellent penetration when shooting through heavy foliage, walls or a common vehicle's metal body and into an opponent attempting to use these things as cover. The 7.62×39mm M43 projectile does not generally fragment when striking an opponent and has an unusual tendency to remain intact even after making contact with bone. The 7.62×39mm round produces significant wounding in cases where the bullet tumbles (yaws) in tissue, but produces relatively minor wounds in cases where the bullet exits before beginning to yaw. In the absence of yaw, the M43 round can pencil through tissue with relatively little injury. Most, if not all, of the 7.62×39mm ammunition found today is of the upgraded M67 variety. This variety deleted the steel insert, shifting the center of gravity rearward, and allowing the projectile to destabilize (or yaw) at about , nearly earlier in tissue than the M43 round. This change also reduces penetration in ballistic gelatin to ~ for the newer M67 round versus ~ for the older M43 round. However, the wounding potential of M67 is mostly limited to the small permanent wound channel the bullet itself makes, especially when the bullet yaws. Operating mechanism To fire, the operator inserts a loaded magazine, pulls back and releases the charging handle, and then pulls the trigger. In semi-automatic, the firearm fires only once, requiring the trigger to be released and depressed again for the next shot. In fully automatic, the rifle continues to fire automatically cycling fresh rounds into the chamber until the magazine is exhausted or pressure is released from the trigger. After ignition of the cartridge primer and propellant, rapidly expanding propellant gases are diverted into the gas cylinder above the barrel through a vent near the muzzle. The build-up of gases inside the gas cylinder