Munmu Z620

The Munmu Z620 is a series of Zhenian and derived  designed and produced by Munmu Arsenal (later Munmu Industries). Although originally intended to be a highly modular weapon, it only shares some common parts between the rifle and light machine gun variants, deviating from the original intention of the design. It was most commonly used as the service rifle of the Greater Eastern Union Defense Forces since the 1960s; although it was later superseded by the Z2000 rifle line as the primary service rifle, it remains in service in many reservist units and foreign armies.

Development
Shortly after the Coup of 1955, the Greater Eastern Union Army issued a demand for a new assault rifle that would replace the existing Z450 rifles in service and altogether be standardized across all military units in the nation, as well as an automatic rifle capable of providing effective fire support when needed. Such line of new rifles would continue the tradition from the Z450 to be chambered in the Munmu 6.8mm rounds while also retain full-automatic fire capability to provide enough firepower should the need ever arise. The two demands, originally anticipated to become two separate projects, became one bigger project altogether when it had been decided that the automatic rifle demand was swapped with a light machine gun that can provide effective, automatic suppression fire on the frontline, and that such rifle would be based on the assault rifle to save development costs and training time. With the initial objective of the rifle's introduction to initiate around 1962, its development was originally dubbed the Type 62 common infantry weapon.

The initial plan behind the series that would later become the Z620 was to build it into a completely modular rifle, with the adjustment and addition of modular parts allowing direct, on-site conversion into any of the variants excluding the variant. While the modular rifle idea became an inspiration for later projects decades later, it had been scrapped during the development of the Z620 series, abandoning the direct, on-site conversion capability between the assault rifle variants and the light machine gun, although a degree of parts commonality has been achieved. During the development process, long-stroke gas-operated rotating bolt mechanism, among other possible options, were decided as the primary operation mechanism for the inside works of the assault rifle; a method was chosen for the primary building method of the rifle to simplify and ease the manufacturing process.

Although its introduction into frontline military service was somewhat later than planned, its first prototypes rolled out in 1962, around the original planned date. With minor refinements in areas such as the iron sights and room for a side rail for additional optics in the future, the first production models saw frontline service at the Greater Eastern Union Army in 1965, both the assault rifles and light machine guns; the Greater Eastern Union Marine Corps received the assault rifles, alongside a revised version of the light machine gun that was a lot closer to the assault rifles, a year later.

Layout
Variants of the Munmu Z620 are piston-driven, air-cooled, magazine or belt-fed (the latter in the case of the Z624 Light Machine Gun variants) and function by a long-stroke gas-operating rotary bolt. The gas-operated long-stroke piston actuates the rotary bolt that is linked to the barrel extension, organized in a manner that allow for the even distribution of the fire load around the barrel. The propellant gases from the cartridge, upon firing, enters the gas cylinder where they initiate the movement of the piston and bolt carrier to the back, while the carrier rotates the bolt to unlock; afterwards a spring-powered ejector ejects the spent cartridge and the casing - all of which can be done automatically.

While initial prototypes of the Munmu Z620 were built from wood and press-manufactured steel, later manufactured variants used an increased percentage of black polymer in areas such as the stock as a weight-saving measure. Although both the rifle and machine gun variants were intended to work without the addition of further optics, there has been room for later iterations to add on via space for the rails on the upper cover. While there had initially been consideration for the usage of rifle grenades in the prototype phase, they have been replaced by flash suppressors in the actual production models.

Ammunition
Akin to its predecessors, all variants of the Munmu Z620 series are primarily chambered in the 6.8mm Munmu rounds, a round that has been standardized since the introduction of the Munmu Z450 in the Second Great War. Although small-caliber high-velocity rounds were also considered, they had been opted out due to penetration issues in medium-to-long ranges; the 6.8 mm Munmu, on the other hand, was capable of delivering effective anti-personnel performance both in close-range combat and in longer-range engagements. Usage of the 6.8mm Munmu rounds allowed for military trainees to begin aiming targets well over 300 meters with the assault rifle variants, although some units fitted with scopes allowed for further targets in the 500-600 meter range.

The assault rifle, carbine and personal defense weapon variants are primarily accustomed to the 30-round box magazine, although extended magazines carrying 40 rounds or even older 10-round box magazines can be used as well. The Z624 Light Machine Gun variant primarily uses a dedicated 200-round ammunition box; however, considering its usage in Marine and Commando units, it has also been designed to be capable of being loaded with the existing 30-round or 40-round box magazines used on the assault rifle variants, with feedback taken from operational service in the late 1960s.

Z622 Carbine
Developed directly from the Z621 assault rifle variant, the Z622 is the first variant of the Z620 series, employing a shorter barrel than the Z621 and featuring a collapsible stock. It, however, uses the same receiver with the Z621, increasing parts commonality. The shorter barrel has resulted in a slower muzzle velocity and therefore a decrease in effective range to around 450 meters; its shorter length, however, has proven effective in close-quarter combat and therefore has increased portability, allowing it to be widely used in mechanized units with limited space for carrying weapons.

Z623 Carbine, Personal Defense Weapon
Developed further from the Z622 Carbine, the Z623 features a collapsible stock and an even shorter barrel and handguard to further shorten the rifle and increase portability. Developed as an alternative to special operations forces as well as military units demanding larger firepower than but lacked the space needed for assault rifles. Aside from the shorter length, its mechanism has been updated for operation in higher rates of fire, while also sporting an improved flash suppressor.

While the initial version has seen service in the Greater Eastern Union Army since 1970, considerable improvements have been made on the platform, with the introduction of on both the receiver and around the handguard as well as updates on the stock, with consideration for operation in units carrying out special operations. Specifically, the Z623A3, the newest iteration of the Z623 introduced in 2011, features mounts for sound suppressors, ceramic coating on metal parts to improve durability and a three-point sling for carrying.

Users

 * Greater Eastern Union Defense Forces: Although many have retired from frontline service, it remains a very common weapon in reservist forces. Much of the existing rifles in service are being replaced by the Z2000 across all branches.
 * Greater Eastern Union Army
 * Greater Eastern Union Navy
 * Greater Eastern Union Air Force
 * Greater Eastern Union Marine Corps