Hypersonic bullets leave large craterlike wounds in flesh, but do not penetrate the skin and flesh as a solid substance like traditional shots, according to a live animal study by military researchers in China. The researchers from an army medical centre in the southwestern municipality of Chongqing fired high-speed 5mm steel bullets at sedated young male pigs to assess the potential impact of hypersonic weapons on the human body. Hypersonic weapons are an intense area of military research, with Russian defence contractor Lobaev Arms saying in 2019 that it was developing a hypersonic rifle that could accelerate a bullet to nearly Mach 6. US hypersonic missile test expected to spur on China’s programme The bullets in the Chongqing experiment were fired at the thigh of each pig and reached a velocity up to 4,000 metres per second (about 13,000 feet per second), or more than 11 times the speed of sound. The shots did not immediately kill the pigs, but shock waves from the bullets caused severe wounds throughout the body, according to a paper published on Monday by the researchers in Acta Armamentarii , an official journal run by the China Ordnance Society. “Extensive damage to many organs can be seen at the time of injury, mainly including the fracturing of bones and bleeding in the intestine, bladder, lung and brain,” said the team led by Wang Jianmin with the Department of Weapon Bioeffect Assessment at the Army Specialty Medical Centre in Chongqing. The pigs were euthanised six hours after the test. Autopsy results suggested the bullet penetrated the thigh at speeds from 1,000 to 3,000 metres per second. “But at a speed of 4,000 metres per second, the projectile failed to penetrate the hindlimb, and a large wound cavity was formed at the impact point,” Wang and his colleagues said. Most guns have a muzzle velocity lower than 1,200 metres per second, or about three times the speed of sound, and in these cases, a bullet will penetrate the skin and flesh as a solid substance, according to Wang. But at hypervelocity, the temperature of a bullet can near melting point. “[The bullet] appears to be on fire when it comes into contact with the skin of the animal, suggesting that the steel ball itself bears a huge force when it hits, and the ball melts and shatters at high temperature,” the paper said. “[It] forms a huge wound cavity similar to a hemispheric pit [crater], which is accompanied by a large amount of tissue spattering.” Under these conditions, the bullet and flesh turn into liquid and gas, so the physical process of the impact needs to be described as fluid mechanics, according to the researchers. The researchers in Chongqing said more animal experiments would be conducted targeting “the head, chest, abdomen and other body parts with more complex structures”. Targets made of soap could produce some similar effects, simulating the movement and energy transfer process of projectiles in soft tissue, according to the researchers. But animals were needed to understand the deadly characteristics of the projectiles on biological targets, they said. Kim Jong-un calls for more ‘military muscle’ after hypersonic missile test Hypersonic weapons are regarded as one of the frontiers of military science. The Lobaev Arms sniper rifle, for example, can hit a target 1km away in half a second, ruling out the need for adjustments for wind, gravity and motion, according to the company. There is no open report that China is developing a hypersonic firearm, but the People’s Liberation Army has funded numerous projects on weapons that can fire small-sized projectiles at speed higher than Mach 5. The Chinese navy, for instance, is investigating whether these hypersonic bullets can be used as part of a ship defence system to intercept enemy drones, missiles or torpedoes. But the development of a hypersonic firearm faces many challenges, according to a Beijing-based researcher studying the physics of explosion. Most existing gun powders could not produce sufficient energy to propel the bullet to such a high speed, and the gun would need a complete redesign with super-tough materials to withstand the explosive force, said the researcher who requested not to be named due to the sensitivity of the technology. How far the bullet would travel remained uncertain if it melted and changed shape in the air, the researcher said. Other issues such as portability and noise could also affect the practical value of such a weapon in battle, he added. China and the US are among the countries that have been developing rail guns that can send hypersonic projectiles over a distance of 200km (124 miles) using electromagnetic propulsion, but reducing the size, wear and energy consumption of these systems remains a challenge.