Daewoo K2
same rifle, butt folded

Daewoo K1A1 (shortened version); buttstock in extended position

Daewoo DR-200 (semi-auto civilian version in .223 Remington), without magazine; note the "post-1994 ban" thumbhole non-folding buttstock, required by current USA laws

	Daewoo K2 rifle	Daewoo K1A1 carbine
Caliber	5.56x45mm NATO
Overall length (butt open / folded)	980 / 730 mm	838 / 653 mm
Barrel length	465 mm	263 mm
Weight	3.26 kg less magazine	2.87 kg less magazine
Magazine capacity	30 rounds
Rate of fire	750 rounds per minute	800 rounds per minute
Effective range	500 meters	250 meters

The K1 assault rifle was developed circa 1983 by the South Korean company Daewoo Precision Industries Ltd (a division of the large industrial corporation DAEWOO International Corp.) as a replacement for the license-built M16A1 rifles, used by the South Korean Army during the 1970s. The improved version, Daewoo K2, appeared circa 1987 and replaced the K1 rifle in production and service. At the present time the K2 assault rifle and K1A1 carbine are the general issue shoulder arms with the South Korean Army. Semi-automatic only, export versions of the K2 rifle, known as a Daewoo DR-100 (pre-1994), DR-200 (post-1994, both chambered for .223 Remington cartridge) and DR-300 (post-1994, chambered for Russian 7.62x39mm cartridge), are intended for the civilian and police markets. The earlier K1 semi-automatic versions were exported from Korea as Daewoo MAX-1 and MAX-2 rifles (both in .223 caliber).
The K2 rifles were designed as improved variations of the M16 rifle. While retaining most of the M16 design features, Daewoo designers replaced the direct gas system of the AR-15/M16 rifle with the more common and reliable gas piston system, and made several other improvements, resulting in very good combat weapon.
Technical description.
The Daewoo K2 is a gas operated, selective fire, magazine fed weapon. The K1 rifle and K1A1 carbine differs from the K2 rifle by different gas system, shorter barrel with different muzzle compensator / flash hider (K1A1 carbine only), and different type of buttstock.
The K2 gas system features a long stroke gas piston, located above the barrel. The bolt group is more or less similar in design to the M16 design, with rotating bolt that have 7 lugs and locks directly into the barrel extension. The cocking handle is attached to the right side of the bolt carrier and reciprocates when gun is fired. Some sources, however, stated that the K1 rifle had the gas system similar to the one found in AR-15/M16 rifles, with no separate gas piston and gases being directed straight into the bolt carrier. The return spring with its guide rod is located behind and partially inside the gas piston rod, and, unlike the M16, does not take space in the buttstock, allowing for folding or completely retractable butt to be used.
The receiver is generally similar in design to the M16 rifle, and is made from two halves, upper and lower, machined from the aluminum alloy forgings, and linked by two cross-pins. It must be noted, however, that Daewoo receivers are NOT interchangeable with any AR-15/M16 type receivers.
The trigger unit is fitted with the 4 position safety / fire selector switch, located at the left side of the receiver, above the pistol grip. The switch has positions for Safe, Single shots, 3 rounds bursts and Full auto fire. It must be noted that the 3 rounds burst counter does not reset itself if trigger is released before all 3 rounds are fired.
The feeding is achieved by using M16-type magazines. Both K2 and K1 rifles incorporate a bolt stop device, which holds the bolt open after the last shot from the magazine is fired.
The sighting system consists of the hooded front sight, mounted on the gas block, and the L-shaped dual aperture rear sight, with one small aperture for daylight conditions and another larger aperture for low light conditions. The range adjustments are made by the rotating knob at the right side of the rear sight block. Maximum range setting is 600 meters. K2 also can be fitted with the see-thru scope rail just ahead of the rear sight block.
The K2 rifle is fitted with the side-folding plastic buttstock and plastic furniture. K1A1 carbine has the retractable steel wire buttstock.

K11 dual-caliber air-burst weapon, left side

K11 dual-caliber air-burst weapon, right side
Caliber: 5.56x45mm NATO + 20x30B mm
Action: Gas operated, rotating bolt for 5.56mm and manually operated for 20mm
Overall length: 860 mm
Barrel length: 310 mm (5.56mm); 405 mm (20mm)
Weight: 6.1 kg (with optics and battery but less magazines)
Rate of fire: ?
Magazine capacity: 30 rounds of 5.56mm and 5 rounds of 20mm
The K11 dual-caliber air-burst weapon was first shown to public in 2009, during DSEI military expo, although information on its development was available since about 2006. The K11 (XK11 during early development) weapon is being developed under direction of the Agency for Defense Development of the Republic of Korea. The K11 shows more than passing similarity to the ill-fated American XM-29 OICW weapon, but it appears that K11 has better chances to see the service - it is believed that first unit of South Korean army could receive the K11 weapons in 2010. This is not surprising, considering the fact that Republic of Korea is among world's leading countries in the field of design and production of advanced micro-electronics, and also has an established defense industry and strong motivation for constant upgrade of military equipment.
As of now, the K11 dual-caliber air-burst weapon is proposed for infantry squad support role, multiplying soldiers capabilities to engage enemy personnel in defilade and soft-skinned vehicles and equipment, using 20mm air-burst grenades with pre-programmed fuse and 5.56mm ammunition for short- to medium range direct fire.
K11 dual-caliber air-burst weapon consists of three major units, linked into one weapon. Those are 20mm multi-shot grenade launcher (which serves as a bone to the system), the 5.56mm automatic rifle with firing controls, and an electronic fire control unit.
The grenade launcher is a manually operated, bolt action weapon that is fed from detachable box magazines. It is built in bullpup layout, with aluminum alloy receiver and titanium alloy barrel. The trigger system of the grenade launcher is mechanically linked to the trigger / selector / safety unit of the integral rifle component. The rifle component is more or less conventional, gas operated, rotary bolt selective-fire weapon which uses M16-type magazines. Its layout is more or less similar to US-made M16 or Korean-made K2 rifles. The trigger unit is a common part between grenade launcher and rifle components, with single safety / fire selector lever providing fire from grenade launcher (single shots) or rifle (single shots or 3-round bursts). The third component is an electronic fire control unit, which includes laser rangefinder, environmental sensors, ballistic computer, and day (optical) and night (IR) sighting channels. The ballistic computer output is fed to the electronic aiming reticle (providing visible point of aim pre-set for proper range) and to the fuse-programming unit in the grenade launcher, which sets the 20mm grenade to explode at specified range, above or to the side of the target, to provide maximum kill effect from explosive fragmenting warhead. At the present time, two types of 20mm ammunition are specified for K11 grenade launcher - the K167 HE air-burst grenade and K168 TP target practice grenade. Rifle component can use any NATO-standard 5.56mm ammunition.

Stg.45(M) - German predecessor to CETME rifles, made at the Mauser Werke in 1945

Early CETME assault rifle prototype chambered for experimental 7.92x40mm cartridge

CETME modelo A assault rifle, chambered for 7.62x51mm reduced load cartridge

CETME modelo B / mod. 58 with 30 rounds magazine

CETME modelo C rifle (semi-automatic only "Sporter" version shown)

data for CETME mod. B / Mod. 58 rifle
Caliber: 7.62x51 mm reduced power load; also 7.62x51mm NATO
Action: delayed blowback
Overall length: 1015 mm
Barrel length: 450 mm
Weight: 4.4 kg
Rate of fire: 550 - 600 rounds per minute
Magazine capacity: 20 or 30 rounds

The Spanish state company CETME (Centro de Estudios Tecnicos de Materiales Especiales - Special Materials Technical Studies Center, now known as Empresa National Santa Barbara) was founded in 1949 to develop various small arms for Spanish army. At about the same time it employed the German arms designer Ludwig Vorgrimler, who worked for the famous Mauser Werke in Germany before and during the World War 2. The Vorgrimler was the designer of the experimental German assault rifle, known as "Gerat 06" or Stg.45(M). This rifle was not manufactured in any quantities, but its design served as a basis for further development at the CETME, and more important, at the another German company, Heckler & Koch, which obtained a license for the Vorgrimler / CETME rifle design circa 1957. This deal later resulted in the famous family of the H&K weapons, like the G3 and HK33 assault rifles, HK21 and HK23 machine guns, MP5 submachine guns and numerous other small arms that achieved a worldwide popularity. All those weapons are built using the delayed blowback system of operation, designed by Vorgrimler and his men at the Mauser in 1945 and refined by CETME.
The initial assault rifle development at the CETME was conducted around proprietary intermediate cartridge, known as 7.92x40mm CETME. This cartridge featured a long and streamlined bullet, made from aluminum. The overall design was found adequate, but cartridge was rejected in favor of the 7.62x51mm round with lighter bullet and a reduced powder charge. Improved rifle entered serial production in 1956 and was adopted by the Spanish army in 1957. In 1958 CETME introduced a slightly improved design, known as Modelo B or Model 58. This rifle was intended to fire 7.62x51mm reduced loads but also could fire the standard 7.62mm NATO, if the bolt group and the return spring are replaced with the appropriate set of parts. In 1964, CETME introduced the Modelo C, which also was adopted by Spanish Army, Navy and Air Force. This rifle was intended to fire only standard, full power 7.62x51mm NATO ammunition. Its key improvements were 4-position diopter sights (instead of the earlier leaf type open sights), wooden handguards instead of earlier steel ones, bipod was made as a separate part and, most important, the chamber was fluted to improve extraction and avoid torn rims and cartridge case failures in harsh environment conditions. Production of the modelo C rifle was ceased in 1976, and in 1980s it had been gradually replaced by its 5.56mm derivative, CETME Modelo L assault rifle.
All 7.62mm CETME rifles are built around Vorgrimlers' roller delayed blowback system. This system employs a two parts bolt with two rollers. The front bolt part (bolt head) is relatively light and has a bolt face with extractor on it. It also has a hollow cavity at the rear, in which an inclined forward end of the rear part of the bolt (bolt body) is inserted. The system features two rollers, inserted from the sides into the bolt head and rested on the inclined forward end of the bolt body (see this diagram; it will pop up in the new window). When gun is fired, the pressure began to move the cartridge back against the bolt face. The rollers, which are extended into the recesses in the barrel extension, began to move inward into the bolt head, due to inclined shape of the recesses. This movement translates into the faster rearward movement of the heavier bolt body, so, at the initial moments of shot, when pressure in the chamber is still high, bolt face moves relatively slow. When pressure drops to a reasonable level, rollers disengage the barrel extension completely and from this moment on the bolt head and the bolt body move backward at the same speed, extracting and ejecting spent case and chambering a fresh cartridge on the way back. All CETME rifles are firing from the closed bolt. The trigger mechanism is hammer fired, and in military versions is capable in semi-automatic and fully automatic modes of fire. On the early models the safety / fire mode selector switch was located above the trigger at the right side of the gun. From the model C the safety / selector switch was relocated to the left side of the gun. The receiver is made from steel sheet stampings, as well as the trigger group housing, which is hinged to the receiver just behind the magazine housing. Early models (prior to Modelo C) were issued with integral folding metallic bipods and open leaf-type rear sights. The Modelo C rifles were issued with wooden handguards and a separate detachable bipods. The rear sights were replaced by the 4 positions diopter sights, marked for 100 - 400 meters range. All rifles featured a wooden buttstock and a folding carrying handle above the receiver. The flash hider of the Modelo C rifles was shaped to accept and launch NATO-standard rifle grenades. Most rifles were issued with magazines of 20 rounds capacity and made of steel, but 30 rounds magazines also were available.

CETME Mod. L assault rifle
Caliber: 5.56x45 mm NATO (.223 rem)
Action: Delayed blowback
Overall length: 925 mm (860/665 mm mod. LC)
Barrel length: 400 mm (320 mm mod. LC)
Weigth: 3.4 kg empty (3.22 kg Mod. LC)
Rate of fire: 600 - 750 rounds per minute
Magazine capacity: 12 or 30 rounds

The Mod. L rifle had been developed by Spanish CETME company (now Santa Barbara SA) as a further derivative of the previous Mod. 58 ad Mod. B rifles. These rifles, in turn, have their roots in WW2 German assault rifle Stg.45, developed by Mauser. After the WW2, some Mauser men moved to the Spain and started to work for CETME, where they developed the Mod. B battle rifle, chambered for 7.62mm NATO cartridge. This rifle later was licensed by Heckler&Koch and beбame the famous G3, but CETME also continued the development. In the mid-1960s men at CETME began to work at smaller-caliber version of the basic rifle, initially called Mod. E. Development was completed in 1980, when first prototype of the Mod. L, chambered for 5.56mm cartridge appeared. Production of the Assault Rifle Mod. L and carbine Mod. LC began in 1984, and it was adopted by Spanish army. In 1999 this rifle was declared obsolete by adoption of the H&K G36E assault rifle.
Like the previus models, CETME Mod. L is a delayed blowback operated, selective fire assault rifle. It has two-piece bolt with two rollers, which are used to accelerate bolt body and to slow bolt head and to hold the cartridge case in chamber until the pressure will drop. The chamber walls are fluted to help the extraction. Overall design is somewhat similar to H&K 33 rifles, but Mod. L is easily distinguishable by larger triggerguard and different (from HK designs) plastic pistol grip and handguards. Sights on Mod. L also are different from HK pattern and rear sight is a simple flip-up "L" shaped leaf with two apertures for 200 and 400 meters. Magazine port also is different from HK pattern and is designed to acceptt M16-type magazines. Carbine Mod. LC differs from the Mod. L by having shorter barrel and telescoping metallic buttstock.

Bofors AK5 - basic version

Bofors AK5B - scoped designated marksmen rifle

Bofors AK5 with M203 grenade launcher

Bofors AK5D - shortened version with Picatinny rail
Caliber: 5.56x45mm NATO
Action: Gas operated, rotating bolt
Length: 1008 mm (Stock Extended), 753 mm (Stock Retracted)
Barrel Length: 450 mm
Weight: 3.90 kg
Magazine: 30 rounds box
Rate Of Fire: 650 rounds per minute
Sweden adopted its first 7.62 mm assault rifle in 1963, as the AK-4. It was a license-built version of the Heckler & Koch G3  rifle, which served well until the adoption of the 5.56 mm ammunition in 1984. After extensive trials, which included designs like the Israeli Galil (made under license by FFV of Sweden), the German HK33, the American M16A1, the Swiss SIG SG-540 and some other designs, the Swedish army finally selected the Belgian FN FNC as its next weapon. The basic FN FNC rifle was modified to suit Swedish requirements, the most notable changes being the omission of the 3-round burst mode of fire, an enlarged trigger guard, a thicker forend and improved, corrosion-resistant finish on all metallic parts. First deliveries were made from FN circa 1986, and domestic rifles began to enter service a year later, made at Bofors' Karl Gustaf factories. The modified FNC rifle, adopted as the AK-5, is now in service with Swedish armed forces.
The AK5 assault rifle is essentially similar to the Belgian FN FNC rifle, except for several modifications. First, the AK5 has no provision for the 3-round burst mode, and will fire only single shots or full auto. Second, the buttstock and handguards are made longer and more suitable for winter conditions, and the charging handle enlarged for better grip when using arctic mittens. Special surface treatment is used for better protection against the elements. The AK5 is manufactured in several modifications, including the basic AK5; the AK5B with 4X telescopic sight (British SUSAT L9A1) and cheek-pad on buttstock, which is issued as a squad-level marksmen rifle; AK5C with Picatinny rail and no open sights; AK5D with the shortened barrel, and integral carrying handle with built-in telescope sight, intended for Commando units and paratroopers; and a grenade-launching version, fitted with American M203 40mm grenade launcher, which is used mostly by Rangers and amphibious forces.

the Interdynamics MKS assault rifle (top, with buttstock unfolded) and MKS carbine (bottom, with buttstock folded)

	MKS rifle	MKS carbine
Caliber	5.56x45 mm
Action	Gas operated, rotating bolt
Overall length (butt open / folded)	868 / 634 mm	751 / 517 mm
Barrel length	467 mm	350 mm
Weight	2,75 kg	2,36 kg
Rate of fire	750 - 1100 rounds per minute
Magazine capacity	30 rounds

The Interdynamics AB company of Sweden attempted to enter an assault rifle market with its MKS rifle in mid-1970s. The Interdynamics MKS assault rifle was more or less conventional in respect to materials and technologies, but layout was not conventional, with box magazine serving as a pistol grip. This layout resulted in shorter overall length when compared to conventional rifles with the same barrel lengths, but seriously compromised ergonomics. Because the standard 5.56mm magazine is significantly deeper 9front to back) than a typical pistol grip, the firing hand's hold and a trigger reach were far from being comfortable. The MKS rifles never were made in any quantities and deserved its place in firearm history more as a curiosity than anything else.
The Interdynamics MKS assault rifle was a gas operated selective fired weapon with rotating barrel locking. Gas system featured a gas regulator. The receiver was made from stamped sheet steel, magazine housing served as a pistol grip. The skeletonized buttstock folded to the right side to save the space. The L-shaped flip-up rear sight has two range settings, for 250 and 400 meters. Carbine version of MKS rifle featured shorter barrel, otherwise being similar to rifle version.

Interdynamics MKR assault rifle

schematic drawing of the 4.5 mm rimfire cartridge for Interdynamics MKR assault rifle
Caliber: 4.5x26 mm Rimfire (special ammunition)
Action: blowback
Overall length: 840 mm
Barrel length: 600 mm
Weight: 3.0 kg less magazine
Rate of fire: no data
Magazine capacity: 50 rounds
The Interdynamics MKR assault rifle was another unsuccessful and unconventional design of the Swedish company Interdynamics AB. Interdynamics MKR assault rifle appeared during 1980s on the top of the "micro-caliber" craze. The idea behind micro-caliber (less than 5 millimeters / .20 inch) ammunition was to achieve high velocity, flat trajectory and good penetration in automatic weapon, and with low recoil. The Interdynamics cartridge was based on .22 Winchester Magnum Rimfire cartridge case, with curved taper and 4.5mm / .177" caliber pointed bullet, made of solid brass. Lightweight bullet (1.58 g / ~24.4 grain) achieved a muzzle velocity of about 1000 m/s (3270 fps). The effectiveness of this bullet was claimed to be on par with 5.56x45mm bullet at the ranges up to 300 meters. Unsurprisingly, the stopping power of such tiny bullet was questionable at its best, and use of rimmed, rimfire ammunition obviously compromised the reliability of the rifle. As a result, Interdynamics MKR assault rifle remained only in prototype stage.
Because of the relatively low power of this ammunition, the MKR gun was made using simple blowback system. Rimmed ammunition was fed from semi-circular magazines, located behind the pistol grip, so the overall layout can be classified as bullpup. Ambidextrous charging handle was located at the top of the plastic receiver. Carbine version of the MKR rifle was similar in design, but had shorter barrel.

7.5mm SIG Stgw.57 assault rifle as used by Swiss army, right side, with bipod attached to forward position

7.5mm SIG Stgw.57 assault rifle as used by Swiss army, left side, with folded bipod attached to rearward position

Semi-experimental 7.62x39 SIG 510-3 assault rifle as made for Finnish army assault rifle trials in late 1950s

7.62x51 NATO SIG 510-4 assault rifle, as made for export

7.62x51 NATO SIG AMT semi-automatic rifle, as made for civilian sales
Caliber: 7.5x55 mm GP11 (Stgw.57) or 7.62x51mm NATO (SIG 510-4)
Action: roller retarded blowback
Overall length: 1105 mm (1016 mm SIG 510-4)
Barrel length: 583 mm (505 mm SIG 510-4)
Weigth: 5.56 kg empty (4.25 rg empty SIG 510-4)
Magazine capacity: 24 rds (20 rds SIG 510-4)

Switzerland began to experiment with intermediate cartridges before the World War 2 and, being a neutral country, closely watched the developments made during and after the war. Being entirely satisfied with the power and accuracy of its 7.5 mm GP11 (7.5x55) cartridge, the Swiss army tried to achieve a full power selective-fire rifle. After a couple of false starts, first with the gas-operated Sk-46 self-loading rifle, and secondly with the most unusual AK-53 blow-forward design, the famous SIG company finally produced a weapon which satisfied the Army in 1955.
This was the 7.5 mm AM-55, a retarded blowback design, developed under the leadership of the Rudolf Amsler. The basic principles of the action were borrowed from German WW2 period Mauser 'Gerät 06H' and Stg.45(M) assault rifles, but with much altering involved. In 1957 the Swiss army adopted the AM-55 as the Schturmgewehr-57, or Stgw.57 for short. Made between 1957 and 1983, the Stgw.57 represented one of the finest and most expensive automatic rifles ever issued to any army in the world. Chambered for full power 7.5 x 55 GP11 ammunition, the Stgw.57 provides long range accurate shooting in semi-automatic mode, necessary for the typical Swiss mountain country, in combination with significant full auto firepower, thanks to its relatively heavy weight, integral bipod and a shrouded barrel. In the modified form, known as the SIG-510, this design was relatively successful, being sold to various South American countries, most notably Bolivia and Chile, chambered for 7.62 mm NATO ammunition. 
The action of the Stgw.57 was derived from the roller-retarded blowback system originated by Mauser engineers in Hitler’s’ Germany. However, the Swiss designers replaced the rollers with the roller-shaped pivoting flaps, interposed between the bolt head and the bolt body. The receiver is made from stamped steel, with a separate trigger unit housing made integral with the pistol grip frame and trigger guard. The fixed barrel has a perforated steel jacket with two mounting points for an integral bipod – one near the muzzle, and another near the receiver. The front part of the barrel is exposed to act as a rifle grenade launcher. To smooth out the excessive recoil generated in full automatic fire, and especially by rifle grenades, the fixed butt-stock is fitted with a recoil buffer. The safety / fire mode selector is located at the left side of the trigger unit. Stgw.57 is fitted with large, T-shaped charging handle and with the folding “winter trigger”, which, when unfolded, extends down below the trigger guard, enabling the rifle to be used in arctic mittens. Since the Stgw.57 was designed with the so-called straight-line layout, the raised sights are mounted on high, folding bases, with the rear sight being micrometer-adjustable from 100 to 650 metres. The Stgw.57 also could be fitted with the special Kern 4X telescope sight. Stgw.57 is fed from curved box magazines, made from steel and containing 24 rounds. The small forend is made from plastic and the gun is fitted with a side-folding carrying handle. Other accessories include the sling, the bayonet, and a special small-capacity magazine for blank grenade-launching cartridges.
Export military versions of the Stgw.57, known as SIG SG-510, were made in 4 basic modifications, of which only one was made in any significant quantities, the SG-510-4. This was chambered in 7.62 x 51 NATO, had a shorter barrel, and non-folding aperture sights. The forend and buttstock were made from wood.
Other versions included the SG-510-1 (exactly the same rifle as the Stgw.57), the SG-510-2 (a lightweight modification of the Stgw.57, also in 7.5 mm), and the more compact SG-510-3, chambered for the Soviet 7.62 x 39 cartridge (produced in late 1950s for assault rifle trials in Finland). Civilian semi-automatic only versions of the Stgw.57 were designated as PE-57 (in 7.5 mm GP11) and SIG AMT (a semi-auto version of SG-510-4 in 7.62 mm NATO).

5.56mm SIG SG-540 assault rifle, with fixed butt and optional bipod

5.56mm SIG-Manurhin SG-540 assault rifle as made in France under license, with side-folding butt


7.62mm SIG SG-542 assault rifle, with fixed butt

5.56mm SIG SG-543 short assault rifle, with side-folding butt

	SIG SG 540	SIG SG 542	SIG SG 543
Caliber	5.56x45mm (.223 Rem)	7.62x51mm (.308 Win)	5.56x45mm (.223 Rem)
Length	950 mm	1000 mm	805 / 569 mm
Barrel length	460 mm	465 mm	300 mm
Weight empty	3.26 kg	3.55 kg	3.0 kg
Magazine capacity	20 or 30 rounds	20 or 30 rounds	20 or 30 rounds
Rate of fire	650-800 rounds/min	650-800 rounds/min	650-800 rounds/min

The SIG SG-540 had been developed by the Swiss company SIG in the mid-1970s as a new,lightweight assault rifle, chambered in then-new small-caliber ammunition (.223 Rem / 5.56mm NATO). The SG-540 was licensed to the Manurhin of France and FAMAE of Chile, and had been temporarily used by French Army (who replaced it with FA MAS rifle in the early 1980s), Portuguese Army and Chilean army, and some other countries, mostly in South America and Africa. 7.62mm NATO version also had been developed, but found no significant sales. The SG-540 itself had not been adopted by Swiss military, but it became the platform for further improvements, which lead to the SIG-550 / Stgw.90 assault rifle. SG-540 currently is in production only by FAMAE company of Chile.
Early SIG prototypes, chambered in 5.56mm ammunition and known as SIG SG-530, were using some forms of roller locking, and thus, were too complicated and expensive to make. To made the rifle as cheap and reliable as possible, SIG designers selected the AK-47 style action, gas operated, with gas piston attached to the bolt carrier, and with rotating bolt with two massive lugs. The recoil spring is located around the gas piston rod, and the bolt carrier attached to the gas piston rod by the removable charging handle. The gas port has gas regulator with two different open and one closed position (latter for firing rifle grenades). The receiver is made from stamped steel and has two major parts, upper and lower, which are connected by pushpins. The barrel is screwed into the upper receiver. The trigger unit has a safety/fire selector switch on the left side of the receiver, with 3 settings: safe, semi-auto, full-auto. If desired, additional module could be installed in the trigger mechanism to allow 3-rounds burst mode. Rear sights are drum-type (like those found on Heckler-Koch rifles). SG-540 has muzzle compensator/flash hider of NATO-standard diameter, so it is possible to launch rifle grenades from the muzzle. The SG-540 has integral folding bipods under the handguard, and can be issued with fixed plastic buttstock or with side-folding tubular metallic buttstock.
The carbine version of the SG-540 is called SG-543 and has shorter barrel. SG-543 can't fire rifle grenades. 7.62mm version of SG-540 is known as SG-542 and visually differs mostly by rectangular magazine of greater depth. SG-542 is chambered for 7.62x51mm NATO ammunition. The civilian version of the SG-540 can fire only in-semi-auto and can be chambered also for .222 Remington cartridge. Other chamberings such as 7.62x39mm Russian (for SG 540) and .243 Winchester (for SG 542) are possible but extremely rare.

Complete family of SIG 55x rifles, top to bottom: SIG SG 550 / Stgw.90, SIG SG 551-LB SWAT, SIG SG 551 and SIG SG 552 SWAT

SIG SG 550 / Stgw.90 assault rifle, left side view

SIG SG 551 SWAT compact assault rifle for police/special forces use, fitted with Trijicon ACOG scope, tactical light, front grip and cheek rest

SIG SG 551 SWAT short assault rifle for police/special forces use, fitted with Trijicon ACOG scope, tactical light and front grip; modern production version with ful-length Picatinny rail on top and folding iron sights.

	SIG SG 550 / Stgw.90	SIG SG 551 (SG 551 LB)	SIG SG 552
Caliber	5.56x45mm	5.56x45mm	5.56x45mm
Length (stock open / folded)	998 / 772 mm	833 / 607 mm (924 / 698 mm)	730 / 504 mm
Barrel length	528 mm	363 mm (454 mm)	226 mm
Weight empty	4.05 kg w/o magazine	3.3 (3.4) kg w/o magazine	ca. 3.0 kg w/o magazine
Magazine capacity	20 or 30 rounds	20 or 30 rounds	20 or 30 rounds
Rate of fire	700 rounds/min	700 rounds/min	780 rounds/min

In the late 1970s the Swiss army began the search for a new, smaller caliber rifle to replace old,full-power 7.5mm Stgw.57 (SIG 510) automatic rifle. Initial tests were done with the 5.6 x 48 Eiger and 6.5 x 48 GP80 ammunition. Prototype rifles were developed by SIG (based on their SG-540 design) and by the state-owned Waffenfabrik Bern (W+F). However, the Swiss army selected a slightly improved version of the 5.56 x 45 NATO cartridge as the 5.6 mm GP90, and further testing proved the superiority of the SIG SG-541 rifle over its W+F rival. In 1983, the Swiss Army officially adopted the SIG SG-541 as the Sturmgewehr-90, or Stgw.90 although due to financial reasons production began only in 1986. Currently, the Stgw.90 is a standard Swiss service rifle.
The Swiss army took its last deliveries of the Stgw.90 in the mid-1990s, but these rifles are still offered for export by the international SIGARMS organization, as well as sold for the civilian market in semi-automatic only versions. In export form this rifle is known as the SIG SG-550. "Carbine" and subcompact "Commando" assault rifle versions are available in the form of SIG SG-551 and SIG SG-552, respectively. Civilian versions of the SIG SG-550 and 551 are known as the Stgw.90 PE in Switzerland or SIG 550-SP and 551-SP when sold for export.
The SIG-550 is often referred as the finest 5.56 mm rifle ever made. It is also, not surprisingly, quite expensive.
Recently, SIG Arms has introduced a civilian / law-enforcement offspring of the SG-550, known as SIG 556. This is a semi-automatic rifle, altered to accept M16-type magazines and fitted with "Americanized" furniture.
Basically, the SIG-550 is a somewhat lightened and refined SIG SG-540/541 rifle. SIG SG-550 is gas operated, with gas piston removably attached to the bolt carrier, and with rotating bolt with two massive lugs. The recoil spring is located around the gas piston rod, above the barrel, and the bolt carrier attached to the gas piston rod by the mean of removable charging handle. The most compact weapon in the line, the SIG SG-552, is similar to SIG SG-551 but it has even shorter handguard and barrel. Due to short barrel and gas piston, SG-552 has return spring relocated to the rear part of the receiver, and thus it has an altered bolt carrier and upper receiver.  The gas port has gas regulator with two different open and one closed position (latter for firing rifle grenades). The receiver of all SG-55x series guns is made from stamped steel and has two major parts, upper and lower, which are connected by pushpins. The barrel is screwed into the upper receiver. The trigger unit has a safety/fire selector switch on the left side of the receiver, with 3 settings: safe, semi-auto, full-auto. If desired, additional module could be installed in the trigger mechanism to allow 3-rounds burst mode. Rear sights are drum-type (like those found on Heckler-Koch rifles). On certain current production models rear sight is replaced with full-length Picatinny style rail with folding back-up reat sight. SIG SG-550 has muzzle compensator/flash hider of NATO-standard diameter, so it is possible to launch rifle grenades from the muzzle. The SIG-550 can be fitted with detachable folding bipods under the handguard, and is issued with side-folding, skeletonized polymer buttstock. Every rifle of SIG SG-550 family can be fitted with proprietary, quick detachable scope mount, although current production rifles are usually fitted with one or more picatinny rails. Swiss Stgw.90 are often seen with 4X fixed power scope, export versions can be equipped with commercial telescope sights, ACOG or "red dot" sights, depending on customer preferences. SIG SG-550 also can be fitted with bayonet. Standard magazine capacity for Swiss military Stgw.90 rifles is 20 rounds, as Swiss tactical doctrine calls for accurate semi-automatic fire, reserving full automatic mode only for emergency purposes. Standard magazines can be clamped together for ease of carry, using integral studs on the magazine walls. For those who might require more firepower, SIG also produces 30-round magazines.

T65 assault rifle
T65K2 assault rifle

T86 carbine

	T65 rifle	T86 carbine
Caliber	5,56x45 mm NATO
Overall length	990 mm	880 / 800 mm
Barrel length	508 mm	375 mm
Weight	3,17 kg empty	?
Rate of fire	700-800 rounds per minute	?
Magazine capacity	20 or 30 rounds

T65 assault rifle was developed at Taiwan state arsenal to replace obsolete 7,62mm M14 rifles of US origin. The T65 rifle closely resembles US-made M16A1 rifle and is probably made on US-supplied machinery, although the Taiwanese rifle has some differences in design and appearance. Reports on original T65 rifle suggested that it performed not satisfactory, so it was improved and became T65K2 (also sometimes referred to as T68). Later on, a T86 carbine was developed - it is very similar externally to US-made M4 carbine although it has piston-type gas action of T65. The last weapon in this line-up is T91 carbine, which can be described as T86 with carrying handle replaced by Picatinny-type accessory rail.
T65 assault rifle is gas operated, selective fired weapon. It uses M16-type two-part aluminum receiver and similar rotating bolt action, although gas system is different - it has short-stroke gas piston, located above the barrel and concealed within handguards. The T65 rifles replaced carrying handle of M16 pattern with rear sight block; otherwise it was similar to M16A1. Starting from T65K2 Taiwanese designers returned the carrying handle (removable on T91 carbine). T65 uses magazines compatible with M16 rifles.
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Vepr assault rifle, left side
Vepr assault rifle, right side
Caliber: 5.45x39 mm
Action: Gas operated, rotating bolt
Overall length: 702 mm
Barrel length: 415 mm
Weight: 3.45 kg empty
Rate of fire: 600-650 rounds per minute
Magazine capacity: 30 rounds
The Vepr ("wild boar" - Ukrainian language) has been announced in 2003 as a new Ukrainian-designed assault rifle. Ukraine is a former Soviet republic and since dissolution of USSR its armed forces used Soviet-era small arms, including the Kalashnikov AKM and AK-74 assault rifles. The Vepr has been advertised as a major improvement over AK-74, but, in fact, it is no more than yet another conversion of standard AK-74 into bullpup layout. The standard AK-74 is stripped from its furniture, and the buttplate is fitted directly to the receiver; polymer cheek rest is fitted to the receiver cover, and pistol grip is fitted ahead of the magazine; the cocking handle is moved to the left side of the forearm, but the safety/fire selector lever remained in the same position, now well behind the pistol grip and almost out of reach when gun is shouldered. Vepr is fitted with adjustable open sights and a standard side mount for day or night scopes. Relatively large red dot scope of Ukrainian manufacture is fitted as a standard. Latest version of the Vepr also feature an integral 40mm underbarrel grenade launcher, with dual trigger arrangement (front trigger controls launcher, rear trigger controls the rifle).
It is yet to be seen if the Vepr will be procured and issued to Ukrainian forces in any numbers, but the claims of "clear superiority to AK-74" from Vepr manufacturers seem to be rather optimistic, to say the least.
PS: there were plenty of conversions of Kalashnikov rifles to bullpup layout before the Vepr, like Russian OC-14 Groza, Finnish Valmet M82, Chinese Type 86 or South African CR-21. None of these had any success so far.

Caliber: 7,62mm NATO (7.62x51mm)
Action: Gas operated, rotating bolt
Length : 1016 mm
Barrel Length: 508 mm
Weight: 4.31 kg empty, without magazine and sling
Magazine: 20 rounds
Rate of fire: 700 rounds per minute (original military version)
The AR-10 rifle, designed by the Eugene Stoner at the Armalite division of the Fairchild Engine and Airplane Corp, seen no significant success at the time it had been introduced, but it still had some historical significance since the AR-10 served as a basis for the further development of the much more successful AR-15 / M16 series rifles. Basically, earliest AR-15 prototypes were no more than a scaled-down AR-10. The AR-10 was intended for the US Army trials for a new battle rifle, to replace the venerable M1 Garand. AR-10, with the first prototype built in 1955, came too late for these trials, and was too unconventional for conservative minds in the US Army, and consequently lost the trials to the T44 rifle, which was adopted in the 1957 as the M14. The AR-10 was ready for mass production by the 1960, but very few were made in USA. A manufacturing license had been sold to the Dutch company Artillerie Inrichtingen. Only Sudan and the Portugal apparently bought some AR-10 rifles for their military, and the production of the AR-10 had been ceased in the early or mid-1960s, with only about 10 000 military AR-10 being ever made.
Some two or three decades later, the reorganized Armalite company brought the modified AR-10 rifle back to civilian and police markets. Unlike the original AR-10, the new AR-10B is a semi-automatic only rifle, and it is available in four basic versions. The AR-10B itself is more or less a copy of the original AR-10, with the similar brown plastic furniture and short buttstock, and with the trigger-like charging handle under the carrying handle. The other three models look more like the scaled up M16A2 derivatives, with the same A2-style furniture, sights, and M16-type charging handles. The AR-10A2 has all the A2 furniture and options, while the AR-10A4 has the "flat-top" style receiver with the Picatinny rail instead of the carrying handle. The AR-10(T) is a target grade rifle, with match barrel and trigger and A4-type flat-top receiver.
Technically, the AR-10 differs very little from its direct derivative, the AR-15/M16, so for a complete description please refer to the AR-15 / M16 article on this site.

T37 experimental rifle

M14 rifle, military issue version with fire mode selector switch installed

Caliber: 7.62x51 mm NATO (.308 Winchester)
Action: Gas operated, rotating bolt
Length: 1120 mm
Barrel Length: 559 mm
Weight loaded: 5,1 kg (6.6 kg M14A1)
Magazine: 20 rounds, detachable box
Rate of fire: 700 -750 rounds per minute
The experience gained by US troops during the Second World war showed that the M1 Garand rifle has a lot of things to be improved. The first was the feeding system with 8-rounds en-bloc clips that does not allowed the refilling of the partially full magazine. Others were excessive length and weight of the rifle. The cartridge used in M1 Garand and known as .30-06 (7.62x63mm) was too long and too heavy, effectively limiting the load of ammunition carried by each soldier. First attempts to improve M1 were made during the war, and numerous experimental modifications in .30-06 were built, mostly using the 20-rounds detachable magazines from Browning BAR M1918 automatic rifle. One of such prototypes was the T20 ("T" means "test") of 1944. T20 was basically the M1 Garand rifle fitted with 20 rounds BAR magazine and with selective fire capability. This prototype latter evolved into the T37 rifle, which had gas cylinder moved back a little and was chambered for newest American prototype cartridge - T65. The T65 was no more than .30-06 case, shortened by 1/2 inch (12 mm), but retaining the original ballistic properties due to modern propellants used. It was slightly lighter and cheaper to made than .30-06, and has long effective range and good potential for accuracy, both desired by US Army. The idea of truly intermediate round was not acceptable to the US Military at that period. In the early 1950s T37 evolved into the T44 experimental rifle, which featured redesigned, self-regulated gas system with short stroke gas piston. Further development and tests lead to the slightly modified T44E4 and T44E5 (heavy barreled squad automatic weapon) prototypes, which were finally adopted by US Army as M14 and M15 rifles in the 1957. The M15, a heavy barreled weapon, however, was never brought into production. It must be noted that T44E4 was extensively tested against the only other entree in the US trials, the T48 rifle (Belgian FN FAL rifle made under license in USA by H&R Inc.). Both rifles passed the trials with equally high results, but US finally settled on the T44 because it was slightly lighter, similar to M1 Garand in manufacturing and operation, and, above all, a "Native American" design.
The contracts to produce M1 rifles were issued to some US companies, such as Thompson-Ramo-Wooldridge (TRW Inc), Harrington and Richardson Arms Co (H&R), Winchester-Western Arms Division of Olin Mathieson (Winchester) and Springfield Armory Inc (Springfield). Production was ceased by US Government in 1964, with some 1 380 000 weapons made. The termination of the production was the result of combat experience in the SE Asia, particularly in Vietnam. The M14 was too long and too heavy to be carried all day long in hot and wet climate. The 7.62mm NATO ammunition was too heavy, limiting the amount of ammunition carried by soldiers on patrols. The selective fire capability was mostly useless, since the M14 was way too light for powerful cartridge it fired, and climbed excessively when fired in bursts. In fact, most of the M14s were issued to troops with fire selectors locked to semi-automatic mode, to avoid useless waste of ammunition in automatic fire. The squad automatic version, known as M14E2, also was not too successful in its intended role. As soon as those deficiencies of the M14 became obvious for US Army Command, they started the search for lighter rifle, and finally settled on the Colt/Armalite AR-15 5.56mm assault rifle, adopting it as the M16A1. M14 was replaced as a first line weapon in the late 1960s, but is still used in small numbers by US Navy. It also served as a platform to build M21 Sniper rifles. Semi-automatic only versions of the M14 rifle are commercially manufactured for civilian and police markets by the Springfield Armory Inc since 1974 under the name of M1A. Some other US companies are assembling the M14-type semi-automatic rifles using military surplus M14 parts kits. Beginning in the early 1970s thousands of M14 rifles were given to several nations under military aid programs. In the 1990s alone, over 100,000 of these rifles have been given away to Estonia, Latvia, Lithuania, the Philippines, South Korea, Taiwan, and Turkey. In USA, for some time M14 was mostly relegated to Honor Guard and similar duties, but during recent campaigns in Iraq and Afghanistan many old M14 rifles were withdrawn from warehouses, dusted off and issued to troops in the field to improve range and lethality of troops armed with 5.56mm weapons. Some M14 rifles are issued as is, some are fitted with new telscope sights to serve as a para-sniper / designated marksman rifles (concept similar to Russian SVD rifle). US Marine Corps also re-issued M14 rifles for use in Designated Marksman role (DMR), and those rifles are fitted with newly made polymer stocks with adjustable buttstocks and pistol grips, and other accessories such as detachable bipods or sound moderators (silencers). Recently US Special Forces, operating under the US Navy flag, stepped forward with the Mk.14 Mod.0 Enchanced Battle rifle, which is an M14 fitted with many new commercially available parts, new stock with adjustable butt and plenty of Picatinny rails, and new accessories such as noise suppressors and optical equipment. The Mk.14 Mod.0 EBR is currently being used by US Navy SEAL's and possibly some other special operation forces within US Military.
In general, the M14 was a comtroversial weapon. It had the accuracy and range of the "old time" military rifles, but was too long, heavy and lacked the automatic fire firepower of a true assault rifle, often required in the modern close combat. Nevertheless, it was a reliable and powerful weapon, often favored by users for high lethality, long range and good penetration - features much appreciated by US soldiers during recent operations in Afghanistan and Iraq.
The M14 is a gas operated, magazine fed, selective fire (originally) design. The gas system is located under the barrel, and has a short stroke (about 1 1/2 inch - 37 mm) gas piston which operates the M1 Garand style action rod. The gas system features an automatic gas cutoff feature, which limits the amount of gases used to operate the weapon. The rotating bolt is quite similar to one found in M1 Garand but it has a roller instead of the simple lug, which connects the bolt to the operating rod. The fire mode selector is located at the right side of the receiver, above the trigger, and could be removed if rifle should not be fired in bursts, or re-installed if required. The rear receiver bridge features the stripper clips guides, so the detachable magazine could be refilled in place by using standard stripper clips. The bolt stop device is incorporated into the left wall of the receiver and holds the bolt open when last round from the magazine is fired. The safety switch is similar to M1 Garand and is located at the front of the triggerguard. Standard sights consist of the blade front sight with two protective "ears" and diopter-type adjustable rear sight, mounted on the rear of the receiver. Barrel is equipped with long flash suppressor. To be used in selective fire mode, M14 can be equipped with light detachable bipod. The M14A1 Squad Automatic rifle differs from M14 in the following: the fire selector is always installed. The standard wooden single-piece stock with semi-pistol grip is replaced by the "straight line" wooden stock with separate pistol grip and with folding front grip under the forearm. The hinged shoulder rest is attached to the buttplate. Special removable muzzle jump compensator is fitted to the barrel, as well as lightweight bipod.