A self-steering bullet has been shown changing direction and speeding up to hit a moving target.

The bullet was developed by America's Defense Advanced Research Projects Agency [Darpo]'s Extreme Accuracy Tasked Ordnance [Exacto] program to "increase hit rates for difficult, long-distance shots".

The agency calls the experiment its "most successful round of live-fire tests to date" and released a video [above], which shows the results.

Initially unveiled at the end of 2014, the bullet has previously been shown changing direction, but this latest test has highlighted its ability to accelerate while in flight and compensate for external factors.

"What was once thought impossible"

The video shows two people using the Exacto bullet. One an experienced shooter using the technology to repeatedly hit moving and evading targets. The second a novice using the system for the first time to hit a moving, torso-shaped target.

The bullet features a real-time optical guidance system to direct it to its target by compensating for "weather, wind, target movement and other factors" that could prevent successful hits.

"True to Darpa's mission, Exacto has demonstrated what was once thought impossible: the continuous guidance of a small-calibre bullet to target," said Darpa program manager Jerome Dunn.

"This live-fire demonstration from a standard rifle showed that Exacto is able to hit moving and evading targets with extreme accuracy at sniper ranges unachievable with traditional rounds.

"Fitting Exacto's guidance capabilities into a small .50-calibre size is a major breakthrough and opens the door to what could be possible in future guided projectiles across all calibres."

The use of the moving bullets, according to Darpa, will "improve sniper effectiveness and enhance troop safety" by allowing snipers to remain further away from targets while retaining their hit rate.

This means that in locations such as Afghanistan, where snipers face tough conditions including dust and high winds, the Exacto technology will be particularly useful.