Army researchers are testing half a dozen ammunition variants in "intermediate calibers," which falls between the current 7.62 mm and 5.56 mm rounds, to create a new light machine gun and inform the next-generation individual assault rifle/round combo.

The weapon designs being tested will be "unconventional," officials said, and likely not one that is currently commercially available.

Some intermediate calibers being tested include the .260 Remington, 6.5 Creedmoor, .264 USA as well as other non-commercial intermediate calibers, including cased telescoped ammo, Army officials said.

If selected by senior leaders, the weapon could resolve a close-quarters weapons debate about calibers that critics say dates to the 1920s and has influenced military small arms ever since.