According to the TechLink Center, the unnamed prototype underwent experimental firings in March 2019 with a "cartridge that contained less than a gram of propellant," and that the firearm's barrel measures 10 inches long.
TechLink assists the US Defense Department in licensing technology it develops in-house to private firms, which can further develop the projects into commercially viable products for the masses.
The center further noted that the prototype's muzzle velocity, the speed with which a bullet or shell leaves the muzzle of a gun, was more than 2,900 feet per second, a record which puts the unnamed firearm ahead of the FN P90, a popular compact weapon.
"The goal is to get rifle-like velocities out of a very small weapon that is high capacity, that's either adaptable for room-clearing or confined spaces," Zac Wingard, a mechanical engineer at the Combat Capabilities Development Command's Army Research Laboratory, told the outlet.
"Like you're getting in and out of vehicles or a subterranean environment, but also applicable for remotely operated systems, so think like perimeter security or ground robot or even a drone."
In order for the weapon to be able to withstand the increase in chamber pressure, researchers adjusted the barrel's design, making it so that the barrel breech locks like a screw.
Task & Purpose further explained that the use of tapered-bore barrels allowed researchers to "translate the increased chamber pressure into additional kinetic energy on the round itself, maintaining lethality at extended ranges."
According to The Drive, the concept behind the tapered barrel, more commonly known as the "squeeze barrel," dates back to World War II-era firearms used by Germany. Although the US Army conducted various tests after the war, it never fielded any of the designs.
Firearms that are currently in use with the US military and hold similarities to the prototype include the 4.7-millimeter Heckler, the Koch MP7 and the 5.7-millimeter FN P90. Users of the weaponry include, but are not limited to, the US Navy's SEAL Team Six and the US Secret Service, The Drive reported.
Another prototype being reviewed by the service is a 24-inch barrel that produces muzzle velocities between 4,600 and 5,750 feet per second. For comparison, a full-size M16 rifle, which is fitted with a 20-inch barrel, only has an average muzzle velocity of roughly 3,150 feet per second, according to The Drive.
It's presently unclear when US troops may actually get their hands on the new technology, as it's still in the R&D phase.