Military technology: Magic bullets | The Economist

The US military is now using a rifle that reads like a science fiction novel: each bullet has a computer chip that calculates trajectory and then blows up when it is near its target, killing the enemy with shrapnel:

via The Economist

The XM25, as the new gun is known, weighs about 6kg (13lb) and fires a 25mm round. The trick is that instead of having to be aimed directly at the target, this round need only be aimed at a place in proximity to it. Once there, it explodes—just like Shrapnel’s original artillery shells—and the fragments kill the enemy. It knows when to explode because of a timed fuse. In Shrapnel’s shells this fuse was made of gunpowder. In the XM25 it is a small computer inside the bullet that monitors details of the projectile’s flight.

A handful of XM25s are now being tested in Afghanistan by the Americans. So far, they have been used on more than 200 occasions. Most of these fights ended quickly, and in America’s favour, according to Lieutenant-Colonel Shawn Lucas, who is in charge of the weapon’s field-testing programme. Indeed, the programme has been so successful that the army has ordered 36 more of the new rifles.

A new equaliser

Each rifle bullet is programmed, before it is fired, by a second computer in the rifle itself. To determine the distance to the target, the gunman shines a laser rangefinder attached to the rifle at whatever is shielding the enemy. If that enemy is in a ditch, a nearby object—a tree trunk behind or to the side of the ditch, perhaps—will do. Looking through the rifle’s telescopic sight, the gunman then estimates the distance from this object to the target. He presses a button near the trigger to add that value to (or subtract it from) the distance determined by the rangefinder.

When the round is fired, the internal computer counts the number of rotations it makes, to calculate the distance flown. The rifle’s muzzle velocity is 210 metres a second, which is the starting point for the calculation. When the computer calculates that the round has flown the requisite distance, it issues the instruction to detonate. The explosion creates a burst of shrapnel that is lethal within a radius of several metres (exact details are classified). And the whole process takes less than five seconds.

Just how the turn-counting fuse works is an even more closely guarded secret than the lethal radius—though judging by the number of failed attempts to hack into computers that might be expected to hold information about it, many people would dearly like to know. Certainly, the trick is not easy. An alternative design developed in South Korea, which clocks flight time rather than number of rotations, seems plagued by problems. Last year South Korea’s Agency of Defence Development halted production of trial versions of the K-11, as this rifle is called, and announced a redesign, following serious malfunctions.

The XM25, in contrast, appears to work well. It is accurate at ranges of up to 500 metres. That is almost as far as America’s main assault rifle, the M-16, can shoot conventional bullets with accuracy. More pertinently, it is nearly double the range of the AK-47, a rifle of Soviet design that is used by many insurgent groups. And according to Sergeant-Major Bernard McPherson, part of the XM25’s development programme in Virginia, it is receiving rave reviews from soldiers in the field.