bolt. Locking occurs by means of lateral flaps located along the sides of the bolt, which are forced outwards (by the angled sides of the hammer) into recesses cut into the receiver body, after which firing occurs when the face of the hammer strikes the rear of the firing pin. The mechanism is simple, rugged and reliable. It features a trigger mechanism that is limited to fully automatic fire only. The bolt is equipped with a spring-loaded casing extraction system, and a fixed insert inside the receiver housing which passes between the feed horns of the bolt serves as the ejector. Spent cartridge casings are ejected downward through an opening in the bolt carrier and receiver. The RPD has a manually operated lever-type safety mechanism that secures the weapon against accidental firing by blocking the bolt catch when engaged. Unlike Degtyarov's earlier firearm patents, the RPD's return spring is located inside the butt. Like many other Russian-made firearms, the chamber and bore are chrome-lined, greatly decreasing the risk of corrosion and jamming. The weapon has a non-removable barrel with a three-position gas adjustment valve used to control the performance of the gas system. It is also equipped with a folding integral bipod, wooden shoulder stock, foregrip and pistol grip. The firearm strips down into the following major groups: the receiver and barrel, bolt, bolt carrier, feed tray and feed cover, the recoil mechanism and the trigger group and stock. Feeding The RPD fires from an open bolt in full auto only. There is no provision for semi-auto fire, although RPD gunners were trained to fire in short bursts to prolong the life of the non-quick-change barrels. The RPD feeds ammunition from the left side using a metallic, open-link, non-disintegrating belt typically holding 100 rounds of 7.62x39 ammunition. Unlike many other belt-fed automatic weapons, where the rounds must be pulled out the rear of the belt and then pushed forward into the chamber, the RPD uses a simpler "push through" design where the rounds are pushed out the front of the belt and into the chamber. At least three variants of the RPD belt were produced. The Russians and Hungarians both produced 50-round belt segments, while the Chinese produced 25-round belt segments. The Russian RPD belts held the rounds in place using the extractor groove. The Hungarians designed a simpler belt that held the cartridges in place using an "L"-shaped tab