Self-Destructing .50 Cal Bullets Could Help Limit Civilian Casualties

The "Limited Range Projectile" would drop out of the air before it could hit a non-combatant. 

A new bullet concept developed by civilian employees of the U.S. Army is designed be less of a danger to bystanders while still keeping bullets lethal. These bullets would self-destruct after a set distance in order to limit the damage it would do beyond whatever the gun is aiming at. 

Brian Kim, Mark Minisi, and Stephen McFarlane—employees at the U.S. Army's Picatinny Arsenal—co-developed the new .50 caliber bullet round. The three were awarded a patent on their "Limited Range Projectile" design in 2015. 

The .50 caliber projectile, that's half an inch in diameter, has been a mainstay of the armed services for almost one hundred years. The bullet is primarily used in the M2 Browning heavy machine gun, which sits on tanks, helicopters, small boats and infantry units. Relatively recently, inventor Ronnie Barrett adopted the .50 caliber bullet to a range of long range sniper rifles. 

The ".50 cal" round has 11,091 foot pounds of energy as it leaves the muzzle of the gun. By comparison, an air rifle has a measly 15 foot pounds of energy, and a 9-millimeter police pistol still has just 383 foot pounds. That kind of energy a .50 cal packs lets it penetrate the walls of dwellings, especially those made of cinder blocks and clay—and keep on going on and going.

This ability to penetrate building material—and armor—is exactly why the Army uses the .50 cal. The problem is that seldom is it that you want to hit anything behind your target, which may include civilians trapped in the battle zone.

The solution is to make a bullet that falls out of the air at a set range. Under the approved patent, there are two ways to make a "Limited Range Projectile". The first is to put a tiny pyrotechnic in the bullet—think something similar to thermite—which ignites when the bullet is fired. 

The next step is make the bullet itself at least partially out of a material that reacts with the pyrotechnic. Bullets are inherently aerodynamic and stable fliers, but deforming will make them unstable, causing them to slow down drastically and eventually tumble out of the air. If you time the reaction properly, the bullet will become unstable at a certain range. 

The second, similar way also incorporates a small pyrotechnic, but enough to start deforming the copper jacket of the bullet in flight. This too makes the bullet aerodynamically unstable. 

The redesign does not mean an less effective bullet. In fact, in a U.S. Army Readiness Development and Engineering Command document, the new bullet designs perform as well as or better than existing .50 caliber bullets in penetrating 3/8" steel armor. 

Right now the bullet is not available in a practical form, and will likely take several more years to develop. There are some questions that need to be answered before an army would be confident enough to field them, questions such as whether or not the burn rate of the pyrotechnic is affected by altitude or other environmental factors. Furthermore, can the bullets be reprogrammed on the fly so that an armored unit moving from an urban to desert combat zone won't be stuck with bullets that are accurate to only 200 yards? 

But if the wrinkles can be ironed out, this "Limited Range Projectile" should help reduce the risk to innocents near the battlefield, a dark side of urban combat that is never going away. 

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