The Swiss Schmidt-Rubin K31 Carbine

By David Tong

The Swiss, knowing that their neutrality might put them at odds with European aggressor nations, have always been a nation of rifleman. To this day every Swiss male serves in the military, either full time or as a reservist, from age 18 to 42, and has a fully-automatic rifle in his residence should an unlikely call to arms ever occur.

They have always been technical innovators in regards to weapon design, even if some of their solutions have not been adopted by any major power. The Karabiner 31 is a case in point.

Messrs. Schmidt (designer of the original rifle action) and Rubin (designer of the smokeless powder cartridge it used) developed a straight-pull, bolt action rifle that the Swiss adopted as their Model 1889. It differs from the usual turn bolt action in that the motion to work the action is a straight pull backward followed by a straight push forward, rather than the up and back, forward and down motion to which the rest of the world is accustomed in its bolt guns.

It does so by using a cam pin, much like that of the AR-15/M16, which imparts rotational motion and primary extraction (the initial removal by rotation of the spent cartridge case) of the bolt from its locked to an unlocked state. The stated advantage of the straight-pull system is to better allow for rapid, repeat fire from concealment or cover without exposing the rifleman's arm and position. The disadvantage of the system is its primary extraction; lacking the normal turn bolt's great rotational leverage imparted by the shooter's arm, a neglected or dirty chamber can theoretically tie up the action. However, most authorities agree that the consistency of manufacture of both rifle and ammo, along with the drilled-in care Swiss NCOs imparted to their troopers made this a non-issue.

The system served through two major variants, the Model 1889, and the later Model 1911, both using the so-called "GP90" 7.5X55mm cartridge. The earliest versions used a round nosed projectile, while later versions used a spitzer bullet. Both were loaded to a maximum average pressure (MAP) of less than 40,000 c.u.p., well below the MAP of the later K31's ammunition. 7.5mm bullets for the rear-locking Model 1889 and 1911 rifles are no longer available.

The K31 made its debut in the Swiss military in 1935, and along with the change in ammunition came changes to the basic rifle action as well. Earlier Schmidt-Rubin rifles featured rear locking lugs, with the majority of the bolt length behind the magazine. To accommodate the higher-powered GP11 cartridge, Swiss ordnance redesigned the bolt system to include forward locking lugs, and its concurrent repositioning of the bolt over the magazine when locked and in battery, thus shortening the action.

Here are the basic specifications of the Karabiner 31:

  • 43.6" OAL
  • 25.65" barrel
  • 6 round detachable box magazine serial numbered to rifle
  • Bayonet (ideally but rarely) serialed to rifle
  • 582,000 produced between 1933-1958

One thing that is not commonly known is that the K31's bullets are not "7.5mm," but actually .307" (essentially 7.62mm). This simplifies reloading, since standard .308" bullets may be used. Interestingly, the Swiss have always specified non-corrosive primers in their Schmidt-Rubin ammo, which with the customary good care means that most surplus rifles will have barrels in far better shape than is the norm for a smokepole of this age.

As was common practice for the day, the K31 had an open, sliding tangent type sight mounted ahead of the receiver, graduated from 100 to 1500 meters. Windage "adjustment" was achieved by drifting a unique, diagonally dovetailed front sight that was available in several sight heights for fine elevation changes. The sights were the then common inverted "V" in front, with a U-notch rear blade.

Unlike rifles manufactured by the major powers, the Swiss rifles did not suffer wartime production exigencies. The quality of the manufacture was never a question, and just one look at the bolt system during field stripping will tell you why. K31s are at once both easier to strip completely, without tools, and more difficult to routinely "field strip," because of the need to line up parts correctly to ensure that the cam system operates.

About the only manufacturing economy the Swiss took was the use of a beech, instead of the earlier walnut, stock and handguard. All metal parts show a very high level of finish machine work, with no rough tool marks evident even below the stock line. The trigger is your typical two-stage military type, but again due to high quality materials, heat-treatment, and proper fitting it breaks cleanly at about 5 pounds after the initial slack is taken up.

Separating the barreled action from the stock shows this quality of manufacture. Both handguard and stock feature a full serial number, and the main bedding block under the receiver ring rests on a metal shim (available in several arsenal thickness') to ensure a stable platform and consistency of bedding for accuracy.

As is usually the case with military bolt guns, the barrel is not free-floated. Instead, there is an inch-long contact point at the forward end of the stock, presumably not just for accuracy but also for bayonet use. Switzerland was probably the last country in Europe still using a bolt action rifle as their principal infantry weapon in the late 1950s.

I have not yet taken the rifle to a rifle range for accuracy testing at measured distances. In informal shooting from the bench (and offhand), it shoots quite well using Swiss surplus GP11 cartridges. Incidentally, this is the same ammo used by individual marksmen in matches in Switzerland, a far cry from what every other nation does. Recoil is about what you'd expect a .30-06 power level round to be like, firm and not helped by the usual curved steel buttplate.

I've fitted mine with a lace-up leather comb riser from Brauer Brothers, which raises my eye for a proper cheek weld, and have also purchased but not yet installed a Picatinny rail that displaces the rear sight leaf. This will enable the use of a long-eye-relief optic much like German WW I and WW II sniper rifles. At this point, I'm thinking about using the Burris 2-7X pistol scope, which will both allow for wide field of view snap shooting in our dense Oregon woods, as well as for the longer-distance precision a fixed power "Scout" scope would not be able to provide.

The rifles themselves are cheap and plentiful as of this writing (2005) and are available from many sources in Shotgun News. You can expect to live with about "80%" condition of the stock furniture, but usually with an immaculate barrel and bolt. Ammo costs are not great, roughly $0.40 per round for Swiss surplus, which is Berdan primed. There are sources of Boxer cases, most notably a short production run of Hornady hunting ammo, in 165 grain BTSP guise, as well as pricey Norma brass.

If you are hankering for something a bit unusual, yet practical for target shooting and hunting most North American game animals, a K31 is far from the worst choice you can make. Depending on your sense of humor, it might be a pretty good one.

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Copyright 2005 by David Tong and/or All rights reserved.