The Korean armed forces are armed with Korean-developed K1- and K2-series 5.56mm weapons; the development and evolution story is not well-known outside of Korea, partly because of heavy secrecy during its development and partly due to the developer’s lack of preserving their development history. This author was able to gather some information during the last 20 years. Herewith is the development history of K1- and K2-series of weapons.
The attempt to develop an indigenous rifle in Korea began during the 1960s; they (Koreans) tried many formats, from a selective-fire conversion of the M1 Garand to a loose copy of the HK G3; calibers were .30-06 or 7.62x51mm NATO. None of them went into actual production. Until the 1970s, South Korea’s industry and economy couldn’t provide Korean made military rifles. Very low on budget and almost without technology and industrial capabilities, it seemed impossible for Koreans to develop and produce their own rifles during this period. Until the 1970s Korean armed forces had to rely completely upon military support from U.S., mostly with M1 Garands/M1-M2 Carbines.
Things changed rapidly during the 1970s. The Korean economy grew surprisingly quickly, and with that growing economy, industrial capacity expanded. There’s one very important thing that happened; Korea began license-building M16A1 rifles.
From 1974 to some unknown point, South Korea had built M16A1 rifles, under license from Colt. That gave not only the first modern assault rifles in quantity to the Korean military (Korean Army/Marines got M16A1s during the Vietnam War from U.S. military aid, but it wasn’t a large enough quantity to arm all Korean active military personnel), but it also gave a tremendous evolution in small arms R&D capabilities.
With those enhanced capabilities, the Korean government hurried their development of an indigenous rifle program in the early 1970s. There were good reasons—from that point in time, U.S. forces in Korea were considerably decreased due to the Nixon doctrine and then the Carter administration’s human rights policy. At that time, Korean government records about human rights and democracy were considered poor, so the Carter administration used the U.S. military presence in Korea as leverage to force improvement in the situation. Koreans suddenly felt it necessary to control and make their own weapons, at least the basics like the firearms. While they could build M16A1s, that wasn’t enough; the original license agreement was 600,000 rifles, and while that number increased considerably later, the point was that Koreans couldn’t make as many M16A1s as they might want. The Korean armed forces themselves needed wartime reserves, and Korea also maintains millions of reservists, who also need to at least have modern rifles. Korea had to pay a license fee for every single M16A1 to Colt, and for a country that is always short on foreign currency (the 1970–1980 Korean economy was far smaller than today’s) that was definitely not a small consideration, especially when they needed to have millions of modern rifles to replace obsolete WWII-era weapons like Garands and Carbines.
With newly formed ADD (Agency for Defense Development) and Busan government arsenal (a new factory was built to make M16A1s at that place: it later became Daewoo Precision), the Korean government seriously began the indigenous rifle program starting in 1972. There’s one strange thing, at least from today’s point of view—from the beginning of the program to around 1975 to 1976, all prototypes made by ADD were in 7.62x51mm NATO caliber, not 5.56x45mm. There were two reasons. First, there was not much 5.56mm ammunition in Korea. Korea couldn’t produce 5.56mm ammo at that time, and almost all U.S.-supplied 5.56mm ammo was used by Korean forces in Vietnam until 1972, and even after that, most of them were used for front line troops. It was hard to spare the large amount of ammo necessary for R&D in Korea. The situation only changed after 1973, when the Poongsan Metal Company (PMC) factory beginning to produce 5.56mm ammo. For a short while after that, the Korean military demanded development of 7.62x51mm NATO rifles rather than 5.56mm. Even the developers didn’t know the exact reason why, but maybe the 5.56mm ammo supply from that early stage of manufacturing wasn’t stable.
All rifle prototypes were numbered in “XB,” like XB-1 or XB-2; until around XB-5, most of them were rather like a 7.62x51mm NATO version of AR-series rifles with odd cosmetic changes. The reason was that most of them used direct gas impingement for operation; all of them had M16-style front sights and many even had M16 handguards. It was obvious to see that the designers tried to use available M16 components as much as possible or copied the components to save development time and resources.
Things changed a lot around the time when prototype XB-6 appeared in 5.56mm, probably around 1976 to 1977. It had a long-stroke gas piston, which was somewhat similar to the AK, and a recoil spring moved from the buttstock to the upper receiver, similar to SIG SG540 series or Stoner 63 series. There were reasons for the change. During the Vietnam conflict, Korean soldiers experienced some unreliability of their M16 rifles, so Korean developers tried to make a more reliable rifle using the long-stroke gas piston. Probably around 1977 to 1978 army began to require the new rifle should have a folding stock, so the recoil spring had to move from the stock.
While the prototype XB-series rifles were developed, some unexpected requirements came from Korean Army special command. When personnel from Spec-Ops Command were invited to see the test-fire of the XB prototypes, they requested the development of a new “Submachine gun” for them. And, they needed that in a hurry.
Spec-Ops Command was desperately in search of new weapons. They used a hodgepodge of weapons, from WWII-era M2 Carbines, M3 Greaseguns, to the brand-new Ingram M10, Israeli Uzi or Colt CAR-15s (XM177s) and M16s, but none of them were in enough quantity for homogenous issue, and maintaining such a variety of weapons was also a logistical nightmare. They wanted to acquire a quantity of standardized personal weapons adequate to their needs.
ADD had to respond to this demand very quickly. Since the “customer” was in a hurry, they (ADD) had no time to develop a completely new weapon. They made a weapon based upon one of their rifle prototypes (probably XB-6 or 7), under the “XB-S” project name (S means short), replaced gas piston with gas tube (so making a direct impingement weapon like the M16), and dramatically reduced its total length. The reason why they used DI, not piston, was also this very short length; they had no time to develop a new short gas piston for a very short barrel (slightly more than 10 inches), while they already had some samples of short barreled CAR-15s to learn how to make a DI system for such barrels. The stock design was very similar to that of the M3 Grease Gun.
This shortened (and DI-converted) rifle became the “SMG, K1” around 1980 to 1981, adopted, manufactured and issued to special operations units first, then to the other MOS who needed short SMG-like weapons, such as tankers, commanders and radio operators. The K1 has 1:12 inch rifling, because during its development there was no plan to adopt 5.56NATO (SS109) ammo in Korean army, and ADD had to adopt the new SMG to then-standard M193 ammo. The K1 series in the Korean military still uses the same rifling, but for export, 1:7.3 inch rifling (same as K2 rifle) is being offered.
While the unexpected SMG version made its appearance first, the development of the original rifle requirement continued. Around the end of the 1970s, the final prototype, XB-7, was developed; from this point the shape of the K2 we now know of was almost complete. Even the XB-7 prototypes had some variations. XB-7A to C were designed; the first one still had a fixed stock, but it soon changed to a side-folding stock similar to FN FAL’s para version. That also changed, since that metal stock was heavy for Koreans as well as expensive. It finally gave way to the side-folding polymer stock we know today.
Around 1982 to 1983, development of the XB-7 was finally completed and received official nomenclature of the K2 rifle. K2 rifle endured many more field tests, and serial production began around 1984. It was officially fielded to frontline units during 1986, and first appeared in public during the 1987 Armed Forces Day Parade.
When K2s began to be mass-produced and fielded, the K1 SMG also experienced evolution. Originally the K1 SMG had a cone-shaped muzzle device, similar to that of AR-18 Shorty; but this had many drawbacks, so around 1984 to 1985, it was replaced with new muzzle device, which is a copy of the XM177’s flash hider. With this change, the K1 SMG became the K1A SMG (some people mistakenly refer to this as the K1A1, but that’s not right). K1, early K1As and early K2s had no locking device on the recoil spring guide, and there were few incidents of “automatic opening” of upper receiver, since the spring guide holds the upper receiver like the AR-18’s spring guide—and without a locking method for the guide, recoil could move the spring guide forward and force the upper receiver to open during shooting. Around 1986 to 1987, both the K1As’ and K2s’ spring guide stud design was changed to have a new locking key to prevent such accidents.
Thus, the design evolution of K1/K2-series weapons was complete around 1986 to 1987, but minor changes kept being applied to the weapons. The gas regulator was re-designed to prevent accidental removal, barrels were changed to be chrome-plated to have longer life, and many parts’ heat treatment methods were improved as the production progressed.
K-series weapons are still in production, and almost a million K1s/K2s have been produced since the early 1980s. Together with the M16A1 license program, Korea produced slightly more than 2 million personal weapons (excluding handguns). Without K-series weapons, that was probably impossible or would have needed much more time to accomplish. The experience of designing the K1 and K2 weapons evolved into the other K-series weapons as production capability expanded.