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The Karabiner Modell 1931 (officially abbreviated to Kar. 31/Mq. 31; commonly but incorrectly known in civilian circles as the K31) is a
magazine A magazine is a periodical literature, periodical publication, print or digital, produced on a regular schedule, that contains any of a variety of subject-oriented textual and visual content (media), content forms. Magazines are generally fin ...
-fed, straight-pull bolt-action
rifle A rifle is a long gun, long-barreled firearm designed for accurate shooting and higher stopping power, with a gun barrel, barrel that has a helical or spiralling pattern of grooves (rifling) cut into the bore wall. In keeping with their focus o ...
. It was the standard-issue rifle of the
Swiss armed forces The Swiss Armed Forces (; ; ; ; ) are the military and security force of Switzerland, consisting of land and air service branches. Under the country's militia system, regular soldiers constitute a small part of the military and the rest are ...
from 1933 until 1958 though examples remained in service into the 1970s. It has a 6-round removable magazine, and is chambered for the 7.5×55mm Swiss ''Gewehrpatrone 1911'' or GP 11, a cartridge with ballistic qualities similar to the
7.62×51mm NATO The 7.62×51mm NATO (official NATO nomenclature 7.62 NATO) is a rimless, straight walled, bottlenecked, centerfire rifle cartridge. It is a standard for small arms among NATO countries. First developed in the 1950s, the cartridge had first be ...
/ .308 Winchester cartridge. Each rifle included a 6-round detachable
box magazine A magazine, often simply called a mag, is an ammunition storage and feeding device for a repeating firearm, either integral within the gun (internal/fixed magazine) or externally attached (detachable magazine). The magazine functions by holdi ...
with matching stamped serial number. A stripper clip can be used to load the magazine from the top of the receiver. The Karabiner Modell 1931 replaced both the Model 1911 rifle and carbine and was gradually replaced by the Stgw 57 from 1958 onwards. Although the Kar. 31 is a straight-pull
carbine A carbine ( or ) is a long gun that has a barrel shortened from its original length. Most modern carbines are rifles that are compact versions of a longer rifle or are rifles chambered for less powerful cartridges. The smaller size and ligh ...
broadly based on previous Swiss " Schmidt–Rubin" service rifles and carbines, the Kar. 31 was not designed by Colonel Rudolf Schmidt (1832–1898) as he was not alive in 1931 to do so. Mechanical engineer Eduard Rubin (1846–1920) was the designer of the 7.5×55mm Swiss ammunition previous Swiss service rifles and the Kar. 31 are chambered for. The Karabiner Modell 31 was a new design by the Eidgenössische Waffenfabrik in
Bern, Switzerland Bern (), or Berne (), ; ; ; . is the ''de facto'' Capital city, capital of Switzerland, referred to as the "federal city".; ; ; . According to the Swiss constitution, the Swiss Confederation intentionally has no "capital", but Bern has gov ...
under Colonel Adolf Furrer (1873–1958). The first 200 Kar. 31s were made in May 1931 for troop trials (serials 500,001 – 500,200), thus the model number of 1931.


Design details


Features

Compared to the previous Schmidt–Rubin series Model 1911 rifle and carbine, the Karabiner Modell 31 bolt and receiver were significantly shortened, allowing for a rifle length
barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden stave (wood), staves and bound by wooden or metal hoops. The word vat is often used for large containers ...
and sight radius, without increasing the overall length of the Model 1911 carbine, moving the rear sight element closer to the eye, and cutting in half the amount of time for the firing pin to strike the cartridge after the
trigger Trigger may refer to: Arts, entertainment and media Fictional entities * Trigger (''Only Fools and Horses''), in the TV sitcom * Trigger Argee, in science fiction short stories by James H. Schmitz * Devil Trigger, a transformation ability of ...
was pulled. The Karabiner Modell 31 barrel has 4 rifling grooves and a
rifling Rifling is the term for helical grooves machined into the internal surface of a firearms's barrel for imparting a spin to a projectile to improve its aerodynamic stability and accuracy. It is also the term (as a verb) for creating such groov ...
twist rate Rifling is the term for helical grooves machined into the internal surface of a firearms's barrel for imparting a spin to a projectile to improve its aerodynamic stability and accuracy. It is also the term (as a verb) for creating such groov ...
. The action itself is only connected to the
stock Stocks (also capital stock, or sometimes interchangeably, shares) consist of all the Share (finance), shares by which ownership of a corporation or company is divided. A single share of the stock means fractional ownership of the corporatio ...
by two screws, one attaching to the recoil lug, with the second attaching to the tang. This allowed the Swiss to eliminate the aluminium barrel mounting collar used in the Schmidt-Rubin series. The trigger was also redesigned. Karabiner Modell 31s are noted for their excellent accuracy and quality for a service rifle. The Swiss armed forces considered individual marksmanship to be of utmost importance. Therefore, the K. 31/Kar. 31 was made to tight tolerances and excellent overall craftsmanship. According to the Swiss Military manual for the Karabiner Modell 31 using standard issue 7.5×55mm Swiss GP 11 ball ammunition in a fixed mounting the expected accuracy of fire at a range of is (R50) in the horizontal (windage) axis and (R50) in the vertical (elevation) axis. Accuracy of fire at a range of is (R50) in the horizontal axis and (R50) in the vertical axis. R50 at a range means the closest 50% of the shot group will all be within a circle of the mentioned diameter at that distance. The employed
circular error probable Circular error probable (CEP),Circular Error Probable (CEP), Air Force Operational Test and Evaluation Center Technical Paper 6, Ver 2, July 1987, p. 1 also circular error probability or circle of equal probability, is a measure of a weapon s ...
method cannot be converted and is not comparable to US military methods for determining rifle accuracy. For reference a 1
minute of arc A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...
(MOA) circle at has a diameter of and at has a diameter of . When the R50 results are doubled the hit probability increases to 93.7%.


Kar. 31 straight-pull action system

The Karabiner Modell 31 is noted for its straight-pull bolt action, meaning that the bolt handle is pulled directly rearward to unlock the action and eject the spent cartridge case in one motion, and then pushing the bolt handle forward again to chamber a new cartridge, cock the striker, and lock the action, rather than being manually turned and pulled back and forth, as in contemporary bolt action service rifles, like the German
Karabiner 98k The Karabiner 98 kurz (; ), often abbreviated Karabiner 98k, Kar98k or K98k and also sometimes incorrectly referred to as a K98 (a K98 is a Polish carbine and copy of the Kar98a), is a bolt-action rifle chambered for the 7.92×57mm Mauser cartri ...
, or the British Lee–Enfield Rifle No. 4. A straight-pull bolt action reduces the range of motion by the shooter, with the goal of increasing the rifle's rate of fire. Unlike the previous Schmidt–Rubin series of rifles, the Kar. 31's locking lugs lock up immediately behind the chamber. This forward positioning of the locking lugs affords several advantages. The entire action is strengthened as the lugs lock into the much thicker forward part of the receiver. Lock-up is also more precise.


Safety

The cocking piece doubles as a
safety Safety is the state of being protected from harm or other danger. Safety can also refer to the control of recognized hazards in order to achieve an acceptable level of risk. Meanings The word 'safety' entered the English language in the 1 ...
and is attached at the rear of the bolt sleeve assembly and secures the
firing pin A firing pin or striker is a part of the firing mechanism of a firearm that impacts the primer in the base of a cartridge and causes it to fire. In firearms terminology, a striker is a particular type of firing pin where a compressed sprin ...
. When the cocking piece ending in a cocking ring is pulled rearward and turned horizontal, the cocking piece sear can be placed in a recessed safety slot in the bolt plug. This slot is shorter than the firing slot so the firing pin cannot protrude past the face of the bolt cylinder. Any contact with the cartridge primer is thus prevented. The safe mode also prevents the action from being cycled hence preventing the bolt from accidental opening. The operating ring is quite large, making it easy to operate with gloves. When the operating ring is in the vertical position and pulled back by cycling the action or cocking it by hand the action is ready to fire.


Ammunition feeding

The Karabiner Modell 31 feeds from a detachable
box magazine A magazine, often simply called a mag, is an ammunition storage and feeding device for a repeating firearm, either integral within the gun (internal/fixed magazine) or externally attached (detachable magazine). The magazine functions by holdi ...
machined to match the cartridge for which the rifle was being chambered, that can hold up to 6 rifle cartridges. The magazine release button is an integral part of the magazine. For reloading the Kar. 31 box magazine was normally not exchanged for another magazine but a unique formed phenolic resin embedded paper
stripper clip A stripper clip (also known as a charger or charger clip, especially in Commonwealth English military vocabulary) is a speedloader that holds several cartridges (usually between 5 and 10) together in a single unit for easier and faster loadin ...
with a tinned metal edge holding six rounds was used. Whereas most chargers or stripper clips only held the rounds at the end of the cartridge cases, the Kar. 31 charger nearly covers the entire cartridge. The charger has a guide slot wide enough for a gloved thumb to force rounds down and into the magazine in one smooth motion. The chargers or stripper clips have to be manually removed before the bolt can be closed. When the last cartridge from the magazine is fired, the follower comes up automatically during cycling locking the bolt open and preventing it from closing reminding the user the Kar. 31 needs to be reloaded.


Trigger

The Karabiner Modell 31 has a two-stage trigger with a noticeable long take up before the trigger engages the sear. This feature aids in preventing premature firing during stressful (combat) situations.


Sights

The standard
iron sights Iron sights are a system of physical alignment markers used as a sighting device to assist the accurate aiming of ranged weapons such as firearms, airguns, crossbows, and bows, or less commonly as a primitive finder sight for optical telescop ...
on a Karabiner Modell 31 are open sights that can be adjusted for both windage and elevation and have a sight radius of . The rear sight is graduated from in increments. The sight line can be adjusted with a front sight adjustment tool. Moving the front post horizontally results in a shift at . To adjust the average height of the point of impact 5 front posts ranging from height in increments are available. The change in impact height from one front sight to the next is at . The standard Kar. 31 iron sight line elevation concept is somewhat unconventional and designed for center hold (point of aim = point of impact) at the and meter settings with GP11 ammunition. Starting at and more distant ranges the shooter should aim below the bottom of the target, so that the front sight's post is just out of the way. The 6 o'clock hold is intended for target shooting at , meaning the sight line is designed to let GP11 ammunition hit over the point of aim on a diameter bulls eye the Swiss military and shooting clubs used for sighting in the Kar. 31, marksmanship training and competitions. A 6 o'clock hold is only good for a known target size at a known distance and will not hold zero without user adjustment if these factors are varied. Combined with GP11 ammunition the and settings can alternatively be used as center holds for and . As the Swiss have a militia army where soldiers sometimes keep their service rifles for a lifetime and also compete with their service rifle. Many aftermarket sights were available: Waffenfabrik Bern made the "S" and "K" (Klammer)
diopter sight A diopter sight is an Iron sight#Aperture sights, aperture sight component used to assist the aiming of ranged weapons, mainly firearms, airguns, and crossbows. Diopters function to precisely align the shooter's eye with the front sight and the ...
s, Wyss makes the "W" diopter and Furter, Haemmerli and Gruenig & Elmiger made special windage and elevation fine-correctors, Sahli and many other made elevation fine correctors and these days a company by the name of Swiss Products in the United States makes a clamp-on diopter which was recently approved for use at official Swiss shooting matches.


Modifications history

During its production run there were several modifications tested, rejected and made to the Kar. 31.


Accessories

Karabiner Modell 31s were issued with slings, muzzle caps, knife-type detachable
bayonets A bayonet (from Old French , now spelt ) is a knife, dagger, sword, or Spike bayonet, spike-shaped melee weapon designed to be mounted on the end of the gun barrel, barrel of a rifle, carbine, musket or similar long gun, long firearm, allowing t ...
, cleaning kits and carrying pouches for stripper clips.


Variants

There were three Karabiner Modell 31 variants that featured telescopic sights. These were the: * Zf. Kar. 31/42, 1.8×9 telescopic sight adjustable from in increments * Zf. Kar. 31/43, 2.8×14 telescopic sight adjustable from in increments The telescopic sights of these models were made by Kern and mounted on production Karabiner Modell 31s chosen for their accuracy offset on the left side of the receiver enabling the shooter to use the standard iron sight line. In the 1950s an elaborate modified variant of the Karabiner Modell 31 was developed for
designated marksman A designated marksman (DM), squad advanced marksman (AD) or squad designated marksman (SDM) is a military marksman role in an infantry squad. The term ''sniper'' was used in Soviet doctrine although the soldiers using the Dragunov SVD were the ...
/
sniper A sniper is a military or paramilitary marksman who engages targets from positions of concealment or at distances exceeding the target's detection capabilities. Snipers generally have specialized training and are equipped with telescopic si ...
use. This rifle was not issued as a Model 31 variant, but as the Zielfernrohr-Karabiner 55 (Zf. Kar. 55) sniper rifle. It featured a more powerful 3.5×23 telescopic sight made by Kern adjustable for bullet drop from in increments. The bullet drop compensation (BDC) adjustment turret is free spinning under grease friction. Like the standard K. 31/Kar. 31 iron sight line elevation concept the BDC adjustment of the telescopic sight is somewhat unconventional and designed for center hold (point of aim = point of impact) at the settings with GP11 ammunition. At more distant ranges the shooter should aim below the bottom of the target for a 6 o'clock hold, so that the reticle's post is just out of the way. The windage adjustment turret of the telescopic sight features more conventional click adjustments. Each full windage increment corresponds to a horizontal displacement of , i.e. the width of a man at (1.5 mil/1.5
The phrase per mille () indicates parts per thousand. The associated symbol is , similar to a per cent sign but with an extra zero in the divisor. Major dictionaries do not agree on the spelling, giving other options of per mil, per mill, pe ...
). The full increments are themselves subdivided into six at (0.25 mil/0.25 ‰) clicks. The Zf. Kar. 55 weighs empty with the telescopic sight mounted and has an overall length of . The Zf. Kar. 55 only has four small parts in common (the cocking piece, the firing pin, the firing pin spring, and the extractor) with the Karabiner Modell 31. The telescopic sight mounts are an integral part of the receiver. The 3.5×23 telescopic sight features an integral quick release mount that connects to the mounts on the left side of the receiver. The entire action of the Zf. Kar. 55 is tilted at an angle of approximately 15 degrees to provide room for the unimpaired loading and ejecting cartridges with the telescopic sight mounted. The tilting of the action and magazine also provided a centered position of the telescopic sight over the action and stock at the cost of widening the rifle somewhat. The barrel fitted to the Zf. Kar. 55 is heavier than the one on the Karabiner Modell 31 and is fitted with a
muzzle brake A muzzle brake or recoil compensator is a device connected to, or a feature integral (ported barrel) to the construction of, the muzzle or barrel of a firearm or cannon that is intended to redirect a portion of propellant gases to counter re ...
. The Zf. Kar. 55 also has a half-stock with a checkered pistol grip instead of a semi-pistol grip and an underfolding integrated
bipod A bipod is a V-shaped portable attachment that helps support and steady a device, usually a weapon such as a long gun or a mortar. The term comes from the Latin prefix and Greek root , meaning "two" and "foot" respectively. Bipods are design ...
. A total of 4,150 Zf. Kar. 55s where manufactured.


Poor stock condition

The poor condition of many stocks was caused mostly by the wearing of crampons ce-cleats that project not only from the sole but the sides of the heelsworn over hobnail boots and rifle drills that were common. The military habit of stacking rifles in threes – often in the snow – also contributes to the 'ragged' appearance of the end of the butt. Postwar beech stocks are more affected than the older walnut ones. Walnut stocks – the material of choice prior to 1946 – were treated with linseed oil and later beech stocks got a shellac protective layer that easily dissolves in alcohol for (arsenal) repairs.


Availability

As of 2010, the Swiss arsenals are long sold out and the rifles now available for sale from
military surplus Military surplus is goods, usually materiel, that are sold or otherwise disposed of when held in excess or are no longer needed by the military. Entrepreneurs often buy these goods and resell them at surplus stores. Usually the goods sold by th ...
vendors in countries around the world are ex-Swiss-civilian owned rifles. The stocks are usually in average condition, but the barrel and bolt assembly are usually in very good condition because the Swiss used a special gun grease known as ''Waffenfett'' instead of gun cleaning oil, and the issued ammunition was non-corrosive. Some Kar. 31s can be found with "troop tags" underneath the steel butt plate at the rear end of the stock, showing its former Swiss government user. Many collectors of the Kar. 31 recovered a small tag of plasticized paper containing the military unit, name and address and national insurance number of the Swiss citizen to whom the rifle was issued. In some cases, collectors have used the information to contact the previous users, and have recounted the details of those encounters on a variety of collector web forums.


Accuracy potential

Karabiner Modell 31s are noted for their excellent accuracy and quality for a service rifle. The Swiss armed forces considered individual marksmanship to be of utmost importance. Therefore, the Kar. 31 was made to tight tolerances and excellent overall craftsmanship. The Swiss Military manual for the Karabiner Modell 31 using standard issue 7.5×55mm Swiss GP 11 ball ammunition in a fixed mounting mentions the expected accuracy of fire at various ranges. The following table lists accuracy statistics for typical in service K31 rifles firing 7.5×55mm Swiss GP 11 service ammunition. The statistics were computed under the 1930s era Swiss method for determining accuracy, which is more complex than Western methods which usually involve firing a group of shots and then measuring the overall diameter of the group. The Swiss method differs in that after a group of shots is fired into the target from a machine rest hits on the outer part of the target are disregarded, while only half of the hits on the inner part of the circles are counted (50% or R50), which significantly reduces the overall diameter of the groups. The vertical and horizontal measurements of the reduced groups are then used to measure accuracy. This
circular error probable Circular error probable (CEP),Circular Error Probable (CEP), Air Force Operational Test and Evaluation Center Technical Paper 6, Ver 2, July 1987, p. 1 also circular error probability or circle of equal probability, is a measure of a weapon s ...
method used by the Swiss and other European militaries cannot be converted and is not comparable to US military methods for determining rifle accuracy. When the R50 results are doubled the hit probability increases to 93.7%. * R50 means the closest 50 percent of the shot group will all be within a circle of the mentioned diameter. * R93.7 means the closest 93.7 percent of the shot group will all be within a circle of the mentioned diameter. For reference a 1
minute of arc A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...
(MOA) circle at has a diameter of and at has a diameter of . The radius of a circle is half its diameter.


Civilian use

Outside of Switzerland, the Karabiner Modell 31 is like other (ex) Swiss service rifles used for target shooting matches. Recreational practice with guns is a popular form of recreation, and is encouraged by the
government A government is the system or group of people governing an organized community, generally a State (polity), state. In the case of its broad associative definition, government normally consists of legislature, executive (government), execu ...
, particularly for the members of the militia. Typical Swiss rifle shooting ''(Eidgenössisches Feldschiessen)'' is done with an (ex) Swiss service rifle at a range of , prone. For this the standard iron sights can be replaced by target shooting diopter and
globe sight A globe sight is a front Sight (device), sight component used to assist the aiming of a gun/device, usually those intended to launch projectiles, such as firearms, airguns, and crossbows. It is found in particular as a front sight element on rifl ...
sighting lines. In other countries the Kar. 31 can often be used in vintage military service rifle matches. Clamp-on sighting options for competition diopter style sights and telescopic sights make it easier to mount more precise aiming means than the standard factory tangent iron sights on the receiver. Many competition shooters are able to achieve 1 MOA shooting groups with unmodified Kar. 31s with the factory tangent iron sight line. To celebrate its introduction in the Swiss armed forces a small commemorative batch of Karabiner Modell 31s was produced 80 years later. In rare instances, the locking lugs of some Kar. 31 rifles can develop cracks that can be visually determined by the naked eye or with the help of a loupe. Rifles with substandard locking lugs should be immediately be withdrawn from shooting and professionally repaired to prevent dangerous situations.Wichtige Mitteilung vom Schweizer Büchsenmacher- und Waffenfachhändlerverband - Gefährliche Probleme beim Karabiner 31 sbv-asa.ch 2008 (German)
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Gallery

File:Baïonnette 1918.JPG, Kar. 31 bayonet M1918 and its frog. File:Magazin K 31.JPG, Kar. 31 box magazine loaded with inert 7.5×55mm Swiss training cartridge. File:K31 phenolic stripper clip.jpg, Kar. 31 Phenolic stripper clips with GP11 ball cartridges. File:K31 Couvre-canon.JPG, Kar. 31 and Kar. 11 muzzle caps for protecting the muzzle. File:K31 Dioptre W+F.JPG, Kar. 31 with W+F diopter rear sight for match shooting. File:K31 Tunnel W+F.JPG, Kar. 31 with W+F globe front sight for match shooting. File:K31-shooting.jpg, Kar. 31 with W+F match shooting sight line. File:K31 Hausse Furter.JPG, Kar. 31 tangent rear sight element with windage and elevation fine-correctors made by Furter. File:K31 culasse open.jpg, Kar. 31 disassembled bolt assembly. Schmidt Rubin k31 otturatore.JPG, Single Kar. 31 bolt


Media

*A video of the Kar. 31 straight pull bolt in action: Media:K. 31/Kar. 31.ogg *In the film '' Shining Through'', a Swiss border guard, with his Kar. 31, shot a
German German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...
sniper firing at Ed and Linda as they were crossing over the Swiss border. *The sniper variant of the K31, the K31/43 appears in the
first-person shooter A first-person shooter (FPS) is a video game genre, video game centered on gun fighting and other weapon-based combat seen from a First person (video games), first-person perspective, with the player experiencing the action directly through t ...
''
Battlefield V ''Battlefield V'' is a 2018 first-person shooter game developed by DICE and published by Electronic Arts. The game is the successor to 2016's '' Battlefield 1'' and the eleventh main installment in the ''Battlefield'' series. It is based on Wor ...
'' which is part of the Summer Update. *The K31 is featured in '' Call Of Duty: Black Ops Cold War'' as a DLC weapon called the Swiss K31 which is part of the Season 3 battle pass. *In the PC horror game '' Mundaun'' the player will eventually gain access to an old bolt action rifle that belonged to main character Curdin's deceased grandfather, most likely a K31.


Users


See also

* Antique gun * M1895 Lee Navy - An American straight-pull bolt-action rifle * Ross rifle - A Canadian straight-pull bolt-action rifle * Steyr-Mannlicher M1895 - An Austrian straight-pull bolt-action rifle


References


External links


Swiss RiflesThe Swiss Rifles Message BoardSurplusrifle.com's articles on the K. 31/Kar. 31Site and tool to determine manufacture year of Swiss Schmidt–Rubin RiflesWebbased Tool to find the manufacture year based on the manufacturer serial number (German Website)The K. 31/Kar. 31 Swiss Service Rifle

Swiss Karabiner 1931
{{Webarchive, url=https://web.archive.org/web/20151107211343/http://candrsenal.com/rifle-swiss-karabiner-1931 , date=2015-11-07 Straight-pull rifles Rifles of Switzerland 7.5×55mm Swiss firearms Articles containing video clips Military equipment introduced in the 1930s Weapons and ammunition introduced in 1933