US military seeks to develop 'silent bullets' Commandos attack during an exercise at Fort Bragg in April 2012. Most bullets make small sonic booms when flying through the air, which to our ears sound like a loud, distinct "crack!" For the Pentagon's special forces, that makes it hard to be sneaky about what they're shooting. Now the commandos want to be sneakier with slower, quieter bullets, U.S. information telecommunication magazine Wired reported Tuesday. According to the magazine, the Special Operations Command (SOCOM) under the U.S. Department of Defense plans to develop rifles in the 5.56, 7.62 and.338 calibers, which will travel at low enough velocities to avoid breaking the sound barrier, thus creating no “crack” noise. In the solicitations, the special forces said the bullet aims to “provide superior covert and stealth capabilities” for not only the military,but police forces and the Department of Homeland Security. Commandos have used subsonic bullets since World War II, though these are mainly effective in smaller guns like the .22 and 9 mm caliber pistols. Breaking the sound barrier also pretty much negates the use of a sound suppressor, or "silencer," which the special forces would likely want to use against militants in Afghanistan and around the world, the magazine said. One solution could be using "polymer cased ammunition" as opposed to brass or steel. Polymer-cased bullets "produce a reliable and consistent powder burn." More specifically, polymer obturates at lower pressures, which means it may be possible to shoot a heavy bullet with less propellant while theoretically not trading for accuracy and range. According to the solicitation, subsonic bullets "experience significant accuracy problems due to excessive deviations in velocity." The gunpowder (or propellant charge) for a subsonic bullet has to be used in smaller quantities than for a normal bullet, and the bullet itself has to be heavier. This results in bullet that is far and away less accurate, doesn't go nearly as far, and "creates lower pressures which ... makes it hard to get a clean burn of the propellant causing rapid fouling of the weapon."