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Manuals


Manuals for the K31-XXI Chassis (and related)

Minor version changes (after the decimal point) correspond to minor changes, essentially cosmetic. Major version changes (before the decimal point) correspond to big important changes.

Historical manuals for the K31 (and related)

These were collected over the years across the Internet, and are believed to be in public domain (a notable exception to most of this site’s contents published under WTFPL); many come from the excellent SwissRifles.com source by the deeply regretted Frank [“Guisan”] van Binnendijk.

 

Ballistics


Ballistic data for your favourite calculator — K31 + GP11 ord.

BC G7 (recommended): 0.276
BC G1: 0.549
Bullet length: 35 mm
Rifling twist: right 270 mm (~10.63″)
V0: 780 m/s @ 7°C
V0 variation: 0.8 m/s per 1°C

Range cards for the typical chassis setup

Sight height: 70 mm
Zero range: 100 m
Cartridge: GP11 Ord.
Click value: 0.1 mrad

[PDF DOWNLOAD]

It looks like this:

(Full user manual for the rangecards)

Serial numbers


K31 modifications history

1934 The firing pin was lightened.
1935 The receiver was made from hardened steel.
1936 The magazine was made from hardened steel.
1941 Stocks made from laminated plywood were tested, but rejected.
1944 Due to supply shortages, Chromium Molybdenum Steel was use in place of Chromium Nickel Steel on various parts. (Recognisable by “+CM” markings instead of the usual “+CN” markings) This experiment proved unsuccessful.
1946 Starting with K31 serial number 868,901, beech wood rather than walnut wood was used for making the stocks.

Serial numbers and manufacturing dates

Source: Manufacture Dates of Swiss Schmidt-Rubin Rifles

Swiss Schmidt-Rubin rifles do not have the date of manufacture stamped on any of the rifle parts, so determining when the rifle (and mismatched parts, if any) were manufactured must be determined from the serial numbers. The definitive work on this subject, and Schmidt-Rubin rifles in general, is Die Repetiergewehre der Schweiz, Die Systeme Vetterli und Schmidt-Rubin, by Reinhart, Sallaz, and am Rhyn (ISBN 3-7276-7102-5, copyright 1991 by Verlag Stocker-Schmid AG, Dietikon-Zuerich, Schweiz), from which the tables given here are adapted.

Model 1931 Carbines (Karabiner) 
Year Quantity Serial numbers
1933 1193 520010-521202
1934 15534 521203-536736
1935 13664 536737-550400
1936 11326 550401-561727
1937 11639 561728-573366
1938 10344 573367-583700
1939 15300 583701-599000
1940 33575 599001-632575
1941 54150 632576-686725
1942 49350 686726-736075
1943 50475 736076-786550
1944 51900 786551-838450
1945 26200 838451-864650
1946 15600 864651-880250
1947 20950 880251-901200
1948 20100 901201-921300
1949 15500 921301-936800
1950 13200 936801-950000
1951 23050 950001-973050
1952 21400 973051-994450
1953 5549
7450
994451-999999
215001-222450
1954 17150 222451-239600
1955 11250 239601-250850
1956 6400 250851-257250
1957 2950 257251-260200
1958 3130 260201-263330

 

Model 1931 Carbines – Private series
Year Quantity Serial numbers
1934 16 ?
1935 500 400001-400500
1936 100 Zoll 401001-401100
1937 150 Zoll
200
401101-401250
400501-400700
1938 150 400701-400850
1939 20 401501-401520
1940 150
530
50
50
400851-401000
401521-402050
402151-402220
402251-402300
1941 300 402301-402600
1942 650 402501[sic]-403150[sic]
1943 350 403151-403500
1944 400 403501-403900
1945 600 403901-404500
1946 837 404501-405337
1947 929
30
405322[sic]-406250
E519767-E519796
1948 400 406251-406650
1949 650 406651-407300
1950 400
50
407301-407700
408001-408050
1951 300
50
407701-408000
408051-408100
1952 300 408101-408400
1953 450
50
408401-408850
409051-409100
1954 200
100
408851-409050
409101-409200
1955 450
100
409201-409650
410151-410250
1956 450 409651-410100
1957 50
300
410101-410150
410251-410550
1958 475 410551-411025
1959 425 411026-411450
1960 300 411451-411750
1961 300 411751-412050
1962 400 412051-412450
1963 50
400
267331-267380
412451-412850
1968-1969 150 various numbers
1971 150
50
269431-269580
269881-269930
Stand (?) 1972 250 various numbers

Note:
Zoll – Customs service

Model 1931 serial number allocation, valid after November 1, 1952 
Serial numbers Allocation
215001-350000 K31 Carbine series, ordered by KTA for KMV
350001-400000 K31 Carbine series
P400001-P450000 Private K31 Carbine series
450001-500000 K31 Carbines with telescopic sights (sniper versions)
500001-500200 Trials versions
E519701-E519900 Various special K31s
519901-519999 Cutaway K31s (running backwards?), last number 519970
520001-520150 Carbine series ordered by KTA, delivered by W+F for special purposes
520081-520100 Ditto, reserved for W+F
520151-999999 Carbine series, ordered by KTA for KMV
after 550651 Hardened magazine boxes
after 540001 Hardened receivers

Notes:
KTA – Kriegstechnischen Abteilung des schweizerischen Militaerdepartements
KMV – Kriegsmaterialverwaltung
W+F – Waffenfabrik

FAQ


The K31 “best” bore diameter: seven-fifty-what?

Almost any Swiss shooter owns a K31. And almost any K31 owner has an opinion as to the “perfect” bore diameter ensuring best precision.

We have an opinion too: it does not matter. We conducted systematic tests of many K31s with Waffenfabrik barrels gauging between 7.51 and 7.54, and found no noticeable correlation between bore diameter and group size.

Furthermore, the diameter is not necessarily an indicator of how used the barrel is; we have measured bore diameters of several brand new carbines of different production lots and years, and found anything between 7.51 and 7.53 — factory new. The official specs are even more generous; according to the Waffenfabrik K31 blueprints, the nominal calibre is 7.51, but production tolerances are ok up to 7.56.

This being said, gauging is useful: barrels which did not have the same diameter over the whole length (one side larger than the other) showed inferior precision compared to fully uniform barrels. Also, barrels gauging 7.55 or above were usually “tired”, and precision started to suffer.

This last remark is only valid for K31s only with Waffenfabrik barrels. Hämmerli barrels (rare, recognisable by the “hammer” marking) gauge larger from factory, and at 7.55 usually show totally convincing precision. Also, standard and free ISSF/CISM 300m carbines (which are usually very precise) chambered for 7.55×55 as a rule are built on .30 cal barrels (the same as for .308 Win or .300 Win Mag), and gauge significantly larger — 7.55 or 7.56 factory new.

In summary: for a Waffenfabrik-barrelled K31, make sure the diameter is below 7.55 and is uniform across the length (same on both the chamber and the business ends). Beyond that — only the target can tell the ultimate truth.

[link]

What is the best scope mount for the chassis?

Short answer: it depends on the scope.

The long answer is at the “Scope + mount, how to choose” page.

What precision can be expected from a K31?

The army manual specifies median (50%) rectangle of 4×6 cm at 300 m at a shooting bench using ordnance GP11 ammo. In other words, at this distance 95% of impacts should land in a 12×18 cm rectangle.

Although many K31 barrels are potentially capable to do better than that, the numbers correspond to a shooting bench, without a real shooter behind the rifle. This being said, with a good optical scope (to minimise aiming errors) and a good ergonomics chassis (to minimise shooter errors / “flyer” shots), it is entirely possible to approach these theoretical limits.

In practice, a good shooter behind a well-equipped carbine, keeping a slow rate of fire (not more than 1 shot per minute, in order not to overheat the barrel), at 300 m can expect 10-shot series of 96 to 98 out of 100 on a FST A10 target. At systematic 98 points or better, one can consider the barrel to be very, very good.

[link]