Shaped charges (also called hollow charges or HEAT charges) can be made quite small and remain lethal to humans, potentially down to roughly 10 mm (or even smaller) in diameter under the right conditions, though effectiveness drops sharply with size due to scaling limits, jet stability, and manufacturing precision.
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Key PrinciplesA shaped charge focuses explosive energy through a conical (or similar) metal liner (often copper) to form a high-velocity jet of metal (typically 5–10+ km/s at the tip). This jet penetrates via hydrodynamic pressure rather than just heat or fragmentation—it punches a narrow, deep hole. Penetration in steel is often ~5–7× the charge diameter (CD) for typical designs, up to ~8–12× CD for optimized high-precision ones (e.g., good liner, high explosive like RDX/HMX/Comp-B, proper standoff).
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Human tissue/bone is far softer than armor steel, so a jet that penetrates even a few cm of steel (or equivalent) can easily go through a body, causing catastrophic internal damage via the hole, pressure waves, and secondary effects (e.g., spall, cavitation).Practical Small SizesExperimental/small-scale examples: Research has tested functional point-focal shaped charges with ~9–10 mm diameters (e.g., copper cone liners, ~14–50g explosive fills like pressed RDX, Comp-B, or Semtex). These penetrated ~30–60+ mm of mild steel.
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Miniaturized designs: Studies have explored ~10 mm scale charges (or even smaller jets) for applications like initiators or specialized tools. Jets from very small cones (liner thicknesses ~0.1 mm) can still form and initiate explosives or penetrate.
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Larger "small" examples: 40 mm grenades (e.g., M433) can incorporate shaped charges capable of defeating light armor. Rifle grenade or small projectile attempts (e.g., ~20–25 mm) have been tried historically but face reliability issues.
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Lethality threshold: A jet capable of ~20–50+ mm penetration (easy for a ~10 mm well-made charge) would be more than enough to kill a human by punching through the torso, hitting vital organs, major vessels, or the spine. Even smaller jets could be lethal if they hit critical areas (e.g., heart, brain, neck arteries). The jet's extreme speed creates massive temporary cavitation and tissue disruption beyond the physical hole.
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Limitations on How Small They Can GetScaling laws and critical diameter: Explosives have a minimum diameter for reliable detonation (critical diameter). Very tiny charges (< ~5–10 mm depending on the explosive) may fail to detonate fully or form a coherent jet. Jet breakup/stretching happens faster at small scales, limiting effective range/penetration.
Manufacture and standoff: Precision liner shaping, uniform explosive fill, and proper standoff (often 2–6 CD) become harder at tiny sizes. Too close = poor jet formation; too far = jet disperses.
Effectiveness drop-off: A very small charge (e.g., sub-10 mm) might produce a narrow jet that penetrates but does limited overall damage compared to fragments/blast from a larger device. Real-world reliability for weapons drops (e.g., early small rifle-grenade attempts were underwhelming).
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Delivery: As a standalone device (e.g., mine, IED, or suicide vest component), very small ones work if placed in contact or near the target. As a projectile (bullet/grenade), stability, fuzing, and barrel/launch constraints make them impractical below certain sizes.
In short, ~10 mm diameter is a realistic lower end for a reliably lethal shaped charge against a human (with tens of grams of high explosive), based on experiments. Smaller is theoretically possible for specialized or experimental setups but becomes unreliable and less effective. These are highly dangerous, specialized devices—not casual explosives—and their use is heavily regulated or illegal in many contexts outside military/industrial applications.