FP-45 Liberator
Guide Lamp Division, General Motors1942–1942Second World War
Also known as M1942
Image credit
- Title
- File:FP-45 Liberator.jpg
- Author
- Rama(attribution required)
- Licence
- CC BY-SA 3.0
- Source
- https://commons.wikimedia.org/wiki/File:FP-45_Liberator.jpg
How Muzzle energy is calculated
E = ½ · m · v²
Inputs
- m14.90 g230.0 grverifiedsource230 gr as published, converted at 1 gr = 0.06479891 g.
- v271.3 m/s890.0 fpsverifiedMeasured with a 127 mm barrel, not this arm's 101.6 mm. Velocity outside the sourced range is not projected.
1 of 2 inputs link to their source.
How Muzzle velocity is calculated
nearest sourced barrel length, no extrapolation
Inputs
- v at 127 mm271.3 m/s890.0 fpsverifiedsource890 ft/s as published, converted at 1 ft/s = 0.3048 m/s.
Assumptions
- This figure belongs to a 127 mm barrel. It is shown because it is the closest measurement that exists, not because it applies here.
1 of 1 inputs link to their source.
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
Inputs
- m_firearm0.45 kg0.9921 lbestimatedsourceConverted from a published 1 lb figure, Wikipedia infobox; no inline citation is given there.
- v_recoil8.984 m/s29.48 fpsestimated
Assumptions
- Propellant gas momentum is excluded: ARMAG does not record charge weights. 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
- capacity1estimatedsourceSingle-shot, break-open action, from the infobox, uncited there.
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
Inputs
- m14.90 g230.0 grverifiedsource230 gr as published, converted at 1 gr = 0.06479891 g.
- v271.3 m/s890.0 fpsverifiedMeasured with a 127 mm barrel, not this arm's 101.6 mm. Velocity outside the sourced range is not projected.
1 of 2 inputs link to their source.
How Sectional density is calculated
SD = mass(gr) / (7000 · diameter(in)²)
Inputs
- mass14.90 g230.0 grverifiedsource230 gr as published, converted at 1 gr = 0.06479891 g.
- diameter11.48 mm0.4520 inverifiedsourceC.I.P. G1, maximum bullet diameter.
Assumptions
- Reported in the conventional lb/in² so it is directly comparable with published figures.
2 of 2 inputs link to their source.
How Power factor is calculated
PF = mass(gr) · velocity(fps) / 1000
Inputs
- mass14.90 g230.0 grverifiedsource230 gr as published, converted at 1 gr = 0.06479891 g.
- velocity271.3 m/s890.0 fpsverifiedMeasured with a 127 mm barrel, not this arm's 101.6 mm. Velocity outside the sourced range is not projected.
Assumptions
- A competition classification defined by the IPSC and USPSA rulebooks, stated in their units. It describes a scoring category, not an effect.
1 of 2 inputs link to their source.
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
- Pistol
- Action
- Break action
- Fire modes
- Single shot
- Operating system
- Manually operated
- Feed
- not recorded
- Designed in
- United States
- Produced in
- Introduced
- 1942
- Production
- 1942–1942
Dimensions and mass
- Mass, empty
Converted from a published 1 lb figure, Wikipedia infobox; no inline citation is given there.
- Magazine, empty
- not recorded
- Length
Converted from a published 5.55 in figure, Wikipedia infobox, uncited there.
- Length, folded
- not recorded
- Width
- not recorded
- Height
- not recorded
- Barrel length
Converted from a published 4 in figure, Wikipedia infobox, uncited there.
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
Operation
- Cyclic rate
- not recorded
- Trigger pull
- not recorded
- Effective range
- not recorded
- Units produced
- not recorded
- Launch price
- not recorded
Chamberings
- .45 ACPprimary1 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.
- FP-45 Liberator141.0 mm5.550 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. FP-45 Liberator records no height, so its outline is drawn at the type's proportion. That height is part of the shape, not a measurement.
Gallery
Image credit
- Title
- File:FP-45 operating instructions.jpg
- Author
- Unknown, presumably a US government employee, given that the weapon was made by and for the U.S. Army
- Licence
- Public domain
- Source
- https://commons.wikimedia.org/wiki/File:FP-45_operating_instructions.jpg
Detail
The FP-45 Liberator is a single-shot, break-open .45 ACP pistol George Hyde designed in May 1942 after a Polish military attaché suggested the concept, built to be dropped in great quantities into occupied territory for use by resistance fighters and partisans. The plan behind it was as much psychological as practical: dropping enough pistols that occupying forces could never recover them all was meant to unsettle those forces regardless of how many were actually used. Its design was deliberately minimal, with just 23 largely stamped and turned steel parts chosen to be cheap and quick to manufacture rather than accurate or durable.
General Motors’ Guide Lamp Division, ordinarily a maker of automotive lighting, manufactured about one million of them between June and August 1942, at a unit cost of roughly two dollars apiece. Its single chamber holds one .45 ACP round at a time, reloaded by hand after each shot, and each pistol shipped with ammunition, instructions and a wooden dowel for punching out the spent case. In practice, US commanders including General Eisenhower’s staff saw little practical value in the mass-drop plan, and fewer than 25,000 of the million produced were ever distributed; most of the remainder went undistributed and were later dumped at sea or melted down for scrap.
Mass, length and barrel length figures on this page come from Wikipedia’s infobox, which carries no inline citation for any of them, so all are recorded as estimated rather than verified. No manufacturer specification sheet was located for a wartime emergency weapon of this kind. No published twist rate was found for this entry.
References
This entry's own bibliography. Every citation key on this page resolves into this list.
- FP-45 Liberator · Wikipedia · 1367556386 · read 2026-09-24 · CC BY-SA 4.0
Last verified 2026-09-24 · review status: draft