Gun design

The current emphasis in gun design is on externally powered weapons for arming light AFVs and helicopters, as this provides several advantages: compactness, reliability and a rate of fire which can be varied to suit the tactical circumstances. The introduction of new ammunition concepts such as those described above does, however, have implications for gun mechanisms. In particular, caseless cartridges offer the promise of considerable simplification. The Russians have experimented with guns using combustible cartridge cases and liquid pro-pellants, the latter including the 23mm AO-23 prototype aircraft gun, although no details are available.

Even more radical concepts will be needed to achieve muzzle velocities in excess of 1,800 m/s (around 2,500 m/s has been calculated to be necessary to defeat the best modern armour). Among those being examined are electromagnetic or rail guns. These use a powerful electromagnetic field to accelerate projectiles up to very high velocities without the need for any cartridge case or propellant. The compactness of the ammunition and the lack of visual or aural signature on firing are clearly attractive, but the current drawback is the massive electrical power required. Some form of breakthrough in generating intense pulses of electricity by means of light and compact batteries or machinery will be required before this becomes feasible even for ships and AFVs, let alone other applications.

A less radical alternative is to use electrothermal-chemical technology. This uses a (relatively) conventional cartridge case and propellant, but the primer is replaced by a plasma generator extending into the propellant. When a strong pulse of electricity is applied to the generator, temperatures of up to 10,000K can be developed. More importantly, the temperature and therefore the burning rate of the propellant are variable, enabling a much better control of the pressure being generated. In a conventional cartridge, it is difficult to achieve a theoretically ideal pressure curve; the plasma generator allows a careful rise in initial pressure to start the projectile safely on its way, building up to achieve the maximum temperature, pressure and velocity which the gun can accept. Test firings have been demonstrated by Bofors using a modified 40mm gun, with the cartridge case being made of synthetic material to achieve electrical isolation. Replacement of the conventional propellant with a material whose gasses have a lower molecular weight would permit even higher velocities. The main problem is the electrical power needed by the plasma generator, not as great as with a rail gun but still too much for current military use.

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