7.7x58SR Type 92
This round was adopted by the Japanese army in 1932 (2592 per Japanese calendar was in use then) as a dedicated medium machine gun round, to improve machine guns performance compared to earlier weapons. It is chambered for a relatively ‘weak’ 6.5x50SR ammunition. Only machine guns were manufactured for this round, and no other weapons for it were made after the end of WW2.
Today it is strictly obsolete.