Karabiner Modell 1931
Karabiner Modell 1931
Waffenfabrik Bern1933–1958Interwar
Also known as K31, Schmidt–Rubin K31
Image credit
- Title
- File:K31 with phenolic stripper clip.jpg
- Author
- GaryArgh(attribution required)
- Licence
- CC BY-SA 3.0
- Source
- https://commons.wikimedia.org/wiki/File:K31_with_phenolic_stripper_clip.jpg
How Muzzle energy is calculated
E = ½ · m · v²
Not calculated: m has no sourced figure yet. Nothing is substituted for a missing input.
No input on this calculation carries a clickable source yet.
How Muzzle velocity is calculated
no sourced velocity for this pairing
Not calculated: muzzle velocity has no sourced figure yet. Nothing is substituted for a missing input.
No input on this calculation carries a clickable source yet.
How Loaded mass is calculated
m_loaded = m_empty + m_magazine + n · m_cartridge
Not calculated: m_magazine has no sourced figure yet. Nothing is substituted for a missing input.
Assumptions
- One magazine, filled to the stated capacity. Spare magazines, optics, slings and lights are the owner’s, not the arm’s.
2 of 4 inputs link to their source.
How Free recoil is calculated
E_recoil = ½ · m_firearm · v_recoil²
Not calculated: v_recoil has no sourced figure yet. Nothing is substituted for a missing input.
Assumptions
- Propellant gas momentum is excluded: ARMAG does not record charge weights (SPEC.md §14). This is therefore a lower bound on the real free recoil, consistent between entries but smaller than a figure that includes the gas term.
- Free recoil: the arm is unrestrained. Stock design, muzzle devices, stance and shooter mass are not modelled, because none of them is a property of the arm.
1 of 2 inputs link to their source.
How Capacity is calculated
as published for the primary chambering
Inputs
- capacity6verifiedsourceDetachable box magazine, normally loaded in place from a six-round charger.
1 of 1 inputs link to their source.
Derived figures
Computed from the sourced values above. Open ƒ on any figure for the formula, its inputs, and the assumptions it makes.
How Momentum is calculated
p = m · v
Not calculated: m has no sourced figure yet. Nothing is substituted for a missing input.
No input on this calculation carries a clickable source yet.
How Sectional density is calculated
SD = mass(gr) / (7000 · diameter(in)²)
Not calculated: mass has no sourced figure yet. Nothing is substituted for a missing input.
Assumptions
- Reported in the conventional lb/in² so it is directly comparable with published figures.
1 of 2 inputs link to their source.
How Power factor is calculated
PF = mass(gr) · velocity(fps) / 1000
Not calculated: mass has no sourced figure yet. Nothing is substituted for a missing input.
Assumptions
- A competition classification defined by the IPSC and USPSA rulebooks, stated in their units. It describes a scoring category, not an effect.
No input on this calculation carries a clickable source yet.
How Magazine dump is calculated
t = (n − 1) / (rpm / 60)
Not calculated: rpm has no sourced figure yet. Nothing is substituted for a missing input.
Assumptions
- Cyclic rate held for the whole magazine, no stoppages, trigger held down. A theoretical figure for comparing mechanisms, not a measured one.
1 of 2 inputs link to their source.
How Sight error at 1 mm is calculated
θ = atan(misalignment / sight radius)
Not calculated: sight radius has no sourced figure yet. Nothing is substituted for a missing input.
Assumptions
- Shows what a stated aiming error costs. The misalignment is the reader’s figure; the site does not claim how well anyone aims.
No input on this calculation carries a clickable source yet.
Specifications
Every row here is generated from the schema, so a figure recorded on this entry cannot be missing from the table — and the same rows, read the same way, are what the comparison shows.
Identity
- Type
- Carbine
- Action
- Straight-pull bolt
- Fire modes
- Single shot
- Operating system
- Manually operated
- Designed in
- Switzerland
- Produced in
- Introduced
- 1933
- Production
- 1933–1958
Dimensions and mass
Sights and rifling
- Sight radius
- not recorded
- Sight height over bore
- not recorded
- Rifling twist
- not recorded
- Twist direction
- not recorded
- Grooves
- not recorded
- Sight graduation
- not recorded
Chamberings
- 7.5×55mm Swissprimary6 rounds
Scale
A to-scale outline against family siblings. The dimensions are sourced; the shape is a representative outline for the type, and says so.
- Karabiner Modell 19311,105 mm43.50 inheight not recorded
Representative outline — the dimensions are sourced, the shape is not. Overall length, and barrel length where recorded, are drawn from this entry's own figures; the profile is a generic one for the firearm type and says nothing about this arm's actual contours. Karabiner Modell 1931 records no height, so its outline is drawn at the type's proportion — that height is part of the shape, not a measurement.
Detail
A straight-pull bolt does not rotate in the shooter’s hand: pulling it back turns the locking lugs through a helical cam inside the bolt sleeve, so the motion is one straight stroke instead of four movements. It is faster, and it is why Switzerland used the layout for eighty years while almost nobody else did.
The 1931 model is a substantial redesign of Rudolf Schmidt’s 1889 action rather than a variant of it. The locking lugs moved from the rear of the bolt to the front, which shortened the receiver by about 60 mm and made the action far stiffer — the reason a K31 shoots as well as it does, and the reason its name is technically wrong.
What it is actually famous for is accuracy. A hammer-forged barrel, a 7.5×55mm GP 11 cartridge made to match standards as a service round, and a militia system in which every man kept his rifle and shot it annually produced a service weapon that competitive shooters still use.
The photograph on this page shows a charger clip inserted into the breech rather than the whole rifle: it is the only freely licensed image on Commons that shows the mechanism, and there is no specimen photograph.
References
This entry's own bibliography. Every citation key on this page resolves into this list.
- K31 · Wikipedia · 1368980364 · read 2026-08-31 · CC BY-SA 4.0
Last verified 2026-08-31 · review status: agent-populated