![]() ![]() It seems clear that new cartridge technologies must be invented to satisfy these conditions. Such low pressures are also insufficient to reliably cycle the action on current gas-operated semi-automatic and automatic rifles, raising a strong possibility of jamming during use. Small chamber pressure can lead to gas leakage from the chamber, and also to a greatly increased chance of having a bullet become stuck in the barrel, rendering the rifle inoperable. ![]() Achieving subsonic velocities requires igniting a very small propellant charge in a rather large cartridge, leading to unsteady burning and erratic chamber pressure. Past experience with subsonic rounds reveals significant accuracy problems, which drives a considerable reduction in effective range. Favored, perhaps, but not easily achieved. However, to date, subsonic ammunition performs reliably only in small caliber silenced pistols, which are unsuited to many missions for which subsonic ammunition would be favored, even transformational. The rise of urban warfare against individuals and small groups suggests that a source of reliable, accurate, and (most of all) quiet subsonic rounds is, to SOCOM, a highly desirable goal. SOCOM-fielded rifles with standard combat loads have muzzle velocities of between Mach 2 and Mach 3, which rather suggests that producing a reliable subsonic round may be a difficult task, especially since the rifles in which these will be fired are designed for the upper velocity of which their cartridges are capable. If a bullet moves faster than that, it generates a sonic boom. In dry air at 20° C (68° F), the speed of sound is about 343 meters per second (1,125 feet per second). ![]() To address this need, SOCOM has issued a Small Business Innovation Research request for proposal for a feasibility study of suitable subsonic rounds. The crack of a rifle shot is the sonic boom of a supersonic bullet, making stealthy ground missions difficult to accomplish. Such sounds have a character that attracts a good deal of attention, which is why the US Special Operations Command (SOCOM) is trying to silence them. Most people have experienced the sonic boom of a skillfully wielded whip, or the closely related crack of a nearby bolt of lightning. ![]()
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