C4 or Composition C4 is a common variety of the plastic explosive known as Composition C.
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C4 is made up of explosives, plastic binder, plasticizer and usually marker or odorizing taggant chemicals such as 2,3-dimethyl-2,3-dinitrobutane (DMDNB) to help detect the explosive and identify its source.[1]
The explosive in C4 is RDX (cyclonite or cyclotrimethylene trinitramine), which makes up around 91% of C4 by mass.[1] The plasticizer is diethylhexyl (5.3%)[1] or dioctyl sebacate and the binder is usually polyisobutylene (2.1%).[1] Another plasticizer used is dioctyl adipate (DOA). A small amount of SAE 10 non-detergent motor oil (1.6%) is also added.[1]
C4 is manufactured by combining the noted ingredients with binder dissolved in a solvent. The solvent is then evaporated and the mixture dried and filtered. The final material is an off-white solid with a texture similar to modelling clay.
C4 has a detonation velocity of 8,092 m/s (26,550 ft/s).[2]
A major advantage of C4 is that it can easily be molded into any desired shape. C4 can be pressed into gaps, cracks, holes and voids in buildings, bridges, equipment or machinery. Similarly, it can easily be inserted into empty shaped charge cases of the type used by military engineers.
C4 is very stable and insensitive to most physical shocks. C4 cannot be detonated by a gunshot or by dropping it onto a hard surface. It does not explode when set on fire or exposed to microwave radiation. Detonation can only be initiated by a combination of extreme heat and a shockwave, such as when a detonator inserted into it is fired.
When ignited with a flame rather than detonated with a primary explosive, C4 burns slowly, so soldiers during the Vietnam War era would sometimes use small amounts of it as a fuel for heating rations. Burning C4 produces poisonous fumes and should be avoided.[3]
Michael Herr in Dispatches, his book about the Vietnam War, relates that a soldier would occasionally ingest C4 from a Claymore mine in order to cause temporary illness so that he would be sent on sick leave. Although the ruse might work with an inexperienced commander, experienced officers were usually aware of the trick and would keep the man on board.
The British military uses a plastic explosive referred to as PE4. Like C4, it is an off-white colored solid and its explosive characteristics are nearly identical to C4. The type and proportion of plasticizer used differs, and PE4 has a slightly greater velocity of detonation, 8,210 m/s (26,900 ft/s). Semtex is a somewhat similar plastic explosive.