九九式軽機関銃
The Type 99 Light Machine Gun was a weapon designed for the [[Imperial Japanese Army]] for [[World War II]].  

The main reason for its development was the Type 99 used a 7.7mm [[cartridge]], while the older Type 96 used a 6.5mm cartridge.  The Imperial Japanese Army wanted to move the standard ammunition of the whole army to "7.7x58mm Arisaka,":http://en.wikipedia.org/wiki/7.7×58mm_Arisaka including a Type 99 Rifle introduced the same year, so that all soldiers could share ammunition. The previous 6.5mm cartridge was not considered powerful enough. 

However, they introduced the cartridge in 1939, just before the start of the war, and not enough of the new weapons could be produced. The Type 99 served alongside the Type 96 it was meant to replace, functionally resulting in just adding another set of ammunition and set of weapons that had to be tracked, rather than simplifying the process. 

"Wikipedia article":http://en.wikipedia.org/wiki/Type_99_light_machine_gun
type 99 light machine gun