Projectile-forming charge

"Shaping" a projectile by the charge

A projectile-forming charge is a special type of shaped charge that is primarily used to destroy armor from a great distance. It is therefore part of armor-piercing ammunition . Other common terms are P-charge or EFP . EFP is the abbreviation for the English term E xplosively F ORMED P rojectile even e xplosively F ORMED or F orged P enetrator. Projectile-forming charges were first developed during World War II .

Structure and effect

Animation of the formation

In contrast to the shaped charges, which are ignited at a distance of about 2.5 to 3 caliber lengths from the target, the distance from the target for the projectile- forming charge is usually at least 50 to 100 caliber lengths in order to enable an optimized formation of the projectile. By increasing the distance from the target and thus the flight time, it is necessary to shape the projectile so that it assumes a stable flight position.

As with the shaped charge, the functional principle is based on the cold forming of a metallic insert using highly explosive explosives ( Munroe effect ). Since the operating principle of the projectile-forming charge corresponds to that of a bullet , the kinetic energy increases with the mass of the penetrator , which is why materials with a high density are used. For the liner , copper (density: 8.92 g / cm³), steel (density: 7.86 g / cm³) or in rare cases also tantalum (density: 16.65 g / cm³) is used ) or uranium (density: 19.16 g / cm³) is used. Copper in particular is used due to its inexpensive production, good ductility and, at the same time, high density.

In the case of the “classic hollow charge”, the explosive is usually shaped around a conical insert, while the insert in the EFP is more spherical or parabolic . With a powerful P-charge, this shape requires a more complex calculation of the insert and charge and also makes production somewhat more difficult. The actual projectile also differs from the shaped charge, which creates a thin spike that is followed by the plunger. In the case of an EFP, a projectile is formed that is more comparable to a normal rifle projectile. As with the shaped charge, the projectile-forming charge is severely undersized, that is, its diameter is considerably smaller than the charge.

Since the shaped charge is designed to be ignited in the immediate vicinity of the target surface, the sting fans out with increasing flight time and thus distance from the target, which reduces the effect on the target. In contrast, an aerodynamically stable penetrator is formed in the projectile-forming charge, which is able to overcome a longer flight distance and achieve the maximum effect.

Some modern EFPs have charges and liners that allow the formation of various projectiles. For example, it is possible to create a long penetrator to optimize penetration performance, an aerodynamically optimized projectile for a greater range or fragmentation comparable to a shot load.

Performance data

The speed of the projectile or penetrator is 2,000 to 3,000 meters per second (m / s), well below that of a military shaped charge, which reaches between 7,000 and 10,000 m / s, but at the same time above that of a conventional mass bullet with a muzzle velocity of up to 1,800 m / s is.

In order to clarify the projectile effect of an EFP, the comparison with a .50 BMG , one of the most powerful cartridges for handguns, which is able to penetrate light armor: the projectile reaches a muzzle velocity of around 900 m / s and a bullet weight of around 50 g a kinetic energy of around 20 kilojoules (kJ). In comparison, a 200 mm copper EFP with a bullet weight of around 3000 g and a speed of up to 2000 m / s achieves a kinetic energy of around 6000 kilojoules (6 MJ).

use

Use in weapon systems

An IED found in Iraq, executed as a P charge

Projectile-forming charges are used today in a wide variety of weapons. For example, the SMArt 155 artillery ammunition has two submunitions that are designed as EFPs. Other “intelligent” artillery or tank shells such as STAFF ammunition or SADARM also use this type of warhead.

The American BLU-108 is a weapon carrier that is used in various guided missiles or bombs such as the AGM-154 JSOW or the CBU-97 Sensor Fused Weapon. The weapon carrier contains four Skeet submunitions designed as EFPs. The use is comparable to that of the SMArt or STAFF.

One version of the TOW 2B anti-tank guided missile has a tandem warhead with EFPs made of tantalum .

EFPs are also used in various types and types of mines. The DM-12 PARM , developed as an off-route mine , uses the principle to combat vehicles from the side, while the MW-1 submunition MIFF (Flat Flat Mine) represents the “classic” anti-tank mine as submunition.

Use as USBV (IED)

EFPs became known through the press at the beginning of the 21st century, as they were increasingly used by insurgents as improvised explosive devices ( IED) against troop transports or tanks after the war in Afghanistan or Iraq . When using EFPs in an urban environment, due to the short distances involved, an optimally shaped penetrator is often not necessary in order to achieve a large damage effect. In addition, these unconventionally manufactured explosive devices usually lack the optimal design and material to achieve an optimal effect. Nevertheless, the poorly protected Humvees of the US Army could be destroyed in this way. The negative experiences with these booby traps accelerated the introduction of better protected wheeled vehicles such as the MRAP or the ATF Dingo in many armies .

Even relatively heavy armored personnel carriers such as the Marder or vehicles specially developed against USBVs do not offer absolute protection due to the high kinetic energy.