Getting back to the original post - you guys do realize that the US were not the only ones fighting against the Japanese during WWII, right?
Take a look at the 7.7 Japanese cartridge and the .303 British. They are very similar rounds. Also, before the war, the British sold a bunch of Vickers MG's and similar to the Japanese and they just copied the cartridge instead of redesigning/rechambering the guns. The Japanese made the 7.7 in rimless (Type 99), semi-rimmed (Type 92) and rimmed versions, depending on the gun it was to be used in (must have be a logistical nightmare!). As the cartridges are so similar this could be where the confusion/rumours got started (at least form a WWII viewpoint).