PRINCIPAL GOVERNMENT PLANTS: Federal Arms Factory, Bern (Waffenfabrik, Hern.)
PRINCIPAL PRIVATE PLANTS: Schweizerische Industrie-A.G., SIG (Neu-hausen and Hämmerli of Lensburg).
PRINCIPAL MILITARY RIFLES: 7.5mm Assault Rifle Model 57, and 7.5mm Model K31.
jPrototype Swiss federal Arms Factory, Bern, 7.5mm Assault Rifle.
Prototype, Swiss Federal Arms Factory, Bern, 7.5mm Short Assault Rifle, right side view
Prototype, Swiss Federal Anns Factory. Ban, 7.5m'« Short Assault Rifle, left side view.
The Swiss have been searching for a suitable replacement for the Schmidt Rubin bolt action rifles for some time. In 1944 a protoiyjie 7.5mm gas-operated rifle was made in limited quantities. In the early 1950s the Swiss Federal Arsenal at Bern developed several selective fire rifles including one for a 7.5mm short cartridge and another for a ^.i^niin short cartridge. The weapon chambered for the 7.5mm short cartridge was similar in concept to the German FG 42 paratroop rifle. After extensive testing the Arsenal designs were dropped and a rifle for the 7.5mm \Iii cartridge designed by SIG was adopted.
A careful appraisal of World War II developments led to the adoption by the Swiss of a new weapons system which would serve their particular tactical requirements. While various medium-range cartridges were rigorously tested, the Swiss concluded thai their high-powered 7.5mm cartridge still suited them best.
The Swiss Industrial Company, popularly known as SIG, under the guidance of its capable designer-director, Rudolf Ainsler. developed three experimental weapons in caliber 7.5mm, the first being the semiautomatic rifle called the
Swiss 7.5mm SIG SK46 Semiautomatic Rifle.
SK46. Outwardly, it resembles the Swiss K31 bolt action rifle. The SK.46 features a remarkably short gas system and up-tilting bolt.
The second weapon to be tested was an assault rifle using a novel breech and blow-forward gas system—AK 53.
The third and only design to be adopted officially was the SIG automatic rifle, identified by the army as StGw 57. (The same weapon offered commercially by SIG was known as the AM55 and now is the SG 510.)
In addition to delivering flat firepower, the SIG rifle has a grenade launcher as an integral part of the barrel, permitting discharge of antitank, antipersonnel, or smoke grenades as required. Use of the rifle is intended to lessen dependency upon such supporting weapons as machine guns, mortars, etc. The versatility of the SIG weapon permits greater flexibility of operation. The individual soldier will, as a consequence, be equipped to contend with a greater variety of situations and be capable of defending a larger perimeter than heretofore expected of him or his weapon.
The delayed blowback or semirigid system of locking is used. The bolt is divided into two separate groups. One group consists of the bolthead which supports the cartridge and which contains the extractor, ejector, and two pivoting, locking cylinders. The other group consists of the plunger shaft which contains the firing pin assembly. This is generally similar to the German StG 45 (M) system.
When the recoil spring sets the plunger shaft into forward motion, the wedge-shaped head of the plunger shaft forces the pivoting, locking cylinders, on either side of the bolt, to swing out from their concealed seats in the bolt-head, and to abut against recesses in the receiver wall, thus securing the bolt. The SIG rifle fires full or serniautomatically from a closcd bolt. The fluted chamber prevents sticking of the case upon firing and is an aid to its rearward movement. The released gases thrust the case against the bolthead, moving it backward .008". This initial force is sufficient to cause the cylinders to pivot out of their geometrically-arranged, locking recesses in the receiver wall and to re-enter their niches in the bolthead. Pressure thus exerted against the shoulders of the wedge front of the plunger shaft causes it to travel backward about 1/4". At this point, the bullet has left the barrel. During the retracting action the plunger shaft absorbs sufficient kinetic energy to propel it rearward in unison with the bolthead, ejecting the expended case. The hammer is cocked and the recoil spring is compressed.
Travel of the bolt mechanism is about 8". Contraction of the recoil spring and special dampers act as brakes to the rearward movement of the bolt mechanism. The compressed recoil spring drives the bolt forward, stripping a cartridge from the magazine and chambering it. As the bolthead encounters the back of the barrel, its forward momentum is halted, but the plunger shaft continues onward until it forces out the pivoting cylinders from the bolthead into their locking recesses in the receiver wall. The weapon is now set for re-firing.
Recoil of the weapon is phenomenally light considering its weight and the use of the full-powered 7.5111m Swiss infantry cartridge (comparable with the U. S. .30-06 round) and is an important factor contributing to easy control of the weapon. By actual test, its recoil is only about one-third that of the Swiss K31 bolt action rifle. Light recoil can be attributed to (1) heavier weight of the SIG rifle, (2) use of a muzzle brake which would, in itself, reduce recoil by 25%, and (3) dispersal of the recoil force by the relatively massive, compounded bolt system which dissipates this force on its long return stroke, as well as by the resistance offered by the recoil spring.
The well-known tendency of automatic rifles to ascend at the muzzle when firing bursts has been minimized in this gun by use of a straight stock designed in line with the longitudinal axis of the barrel to reduce leverage force against the shoulder created by recoil. This control is evident when firing full automatic from the hip or in prone position. It is particularly noticeable when firing from the shoulder where control has always been difficult. Minimizing "climb" and recoil reduces (he tendency lo obscure the target, promising more accurate delivery of rapid fire.
Accuracy of the SfG rifle is, at least, on a par with their very fine bolt action Kgi rifle and is one of its outstanding features. A special accuracy test in which a SIG rifle was selected at random, placed in a machine rest, and fired at 100-meter target, resulted in a (-> shot 2%" group. At the conclusion of controlled tests conducted at Swiss Army shooting schools, marksmanship badges were awarded to 19% of the recruits firing the K31 bolt action rifle, as compared with 29% using the SIG StGw 57 automatic assault rifle—evidence ol easy mastery and control of the weapon by men not particularly skilled in shooting.
Swiss Model 57 7.5mm Assault Rifle.
The StGw 57 is equipped with a carrying handle as well as an adjustable, folding bipod. Normally the bipod is located in the forward position near the muzzle. However, the bipod can be quickly relocated centrally under the barrel for a greater arc of fire and wider maneuverability.
A composition rubber butt imparts a certain amount of resiliency to the stock during grenade launching when the butt is backed up by a solid object, such as a building wall, curbstone, etc.
In view of the straight-line design of the stock, the sights are located high on the weapon; however, tliey may be folded down out of the way. For the
Swiss St(iw Model 57 Assault Hifte, Stripped.
first time the Swiss have, in this particular instance, adopted a rear aperture sight.
I'lie SIC automatic rifle was designed for low-cost mass production, making almost complete use of sheet metal stampings. Plain carbon steels are used for
Holt of Swiss 7.5rnm Model 57 Assault Rifle. Top, boll disassembled; Bottom, bolt assembled.
the few machined parts since the supply of high-alloy steels is, generally, the first to become critical during shortages.
It has proved economically feasible, as well as detrimental to the formation of an arms cartel, to manufacture weapons in parts (barrels, receivers, magazines, screws, stocks, etc.) in many different plants throughout Switzerland. Decentralization of industry serves also as an effective defense measure in the event of attack. SIG lets contracts on their assault rifle to more than 200 subcontractors who produce the various components, shipping go% of their output to the Swiss Federal Arsenal in Berne for final assembly. The remaining 10% of output is assembled by SIG as a control check on the production of the component parts.
The StGw 57 is relatively easy to maintain. Field stripping is fast and simple. To do so, remove butt stock from receiver by depressing bolt catch and rotating stock counterclockwise about one-eighth turn; then withdraw it back out of the receiver. Withdraw the recoil spring. Remove operating handle by pulling it rearward out of the receiver. The bolt assembly now protrudes about Yt" from the receiver. Grasp it firmly and remove it from the receiver. Then remove trigger mechanism. The gun can be reassembled by reversing these steps.
SPECIFICATIONS OF THE SWISS STGW 57 ASSAULT RIFLE Caliber: 7.5mm Swiss Total length of weapon: 43.3". Length of barrel including muzzle brake: 27.17". Length of barrel excluding muzzle brake: 20.47". Depth of rifling: .0098". Number of grooves: 4. Width of rifling: .1456". Weight of barrel: 3.04 lbs. Weight of weapon without magazine: 12.56 lbs. Weight of magazine fully loaded with 24 rounds: 1.98 lbs.
A version of the StGw 57 is the SG 510. This is not a Swiss Service rifle; it is a development of the StGw 57 which was developed by SIG as a commercial venture. The SG 510 was made in several varieties; the SG 510-4 was chambered for the 7.62mm NATO cartridge and the SG 510-3 was chambered for the Soviet 7.62mm M43 carbine.
SIG has worked for a number of years on development of a new .223 (5.56mm) military rifle based on the action of the StGw 57. A number of models were produced prior to the appearance of the SG 530-1. This rifle is manufactured principally of stampings and fabrications. There are two versions: with plastic fixed stock and with metal folding stock.
System of operation: Delayed blowbark, selective fire
Length overall: W/fixed stock—39.5 in.
W/folding stock—stock folded—30.8 in. Barrel length: 18.1 in.
Feed device: 30-round, staggered row, box magazine
Sights—front: Protected post rear: Aperture adjustable from 100 to 300 meters
W/folding stock—8.44 lb. Cyclic rate: 550-600 r.p.m.
This rifle breaks open like a shotgun for stripping. A combined Hash suppressor/grenade launcher is screwed 011 the end of the barrel.
SIG .223 Model 530-1 Rifle field stripped.
SIG SG 510-4 Rifte with scope.
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