The 7.7 x 58mm Japanese enjoyed mild popularity among American hunters after World War II, when surplus military rifles were imported to the U.S. The cartridge was adopted by the Japanese military in 1939 in the Model99 Arisaka rifle as a replacement for the older 6.5mm cartridge but both remained in service during World War II. Some handloaders form 7.7 cases from .30-06cases, but since the latter has a slightly smaller base diameter the best bet is to buy Normaammunition and reload those cases. Ballistically, the 7.7 falls between the .300 Savage and .308 Winchester. Bullets of .311" diameter (same as the .303 British) are available from Hornady, Sierra, and Speer. A 150 grain spitzer pushed to 2500 fps with H414, H335, or H4895 is a good choice for deer size game at close to medium ranges. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.