It has often been said that historical tests like those conducted by the "Pig Board" have shown the "ideal" caliber range for infantry rifles/carbines to be 6.5-7mm. Yet, every country that adopted 6.5mm or 7mm eventually abandoned them in favor of 7.62mm or larger calibers. In most instances, economics and/or politics played a major role. However, those don't seem to have been factors in the decision by Imperial Japan to switch from 6.5mm to 7.7mm.
The only published reason that I've ever seen is that combat experience resulted in dissatisfaction with the terminal effectiveness of 6.5 Jap. This is a bit puzzling to me, inasmuch as the standard, 139gr ball projectile has a configuration and rearward weight bias which seems like it should produce fairly rapid onset of yaw in soft tissue.
Can anybody:
1. Cite authoritative source(s) of the actual reason(s) for the switch from 6.5mm to 7.7mm?
2. Cite anecdotal reports of incapacitation effect of 6.5 Jap ball ammo, either by shooters or shootees?
3. Post the ballistic gelatin wound profile of WWII 6.5 Jap ball ammo?
The only published reason that I've ever seen is that combat experience resulted in dissatisfaction with the terminal effectiveness of 6.5 Jap. This is a bit puzzling to me, inasmuch as the standard, 139gr ball projectile has a configuration and rearward weight bias which seems like it should produce fairly rapid onset of yaw in soft tissue.

Can anybody:
1. Cite authoritative source(s) of the actual reason(s) for the switch from 6.5mm to 7.7mm?
2. Cite anecdotal reports of incapacitation effect of 6.5 Jap ball ammo, either by shooters or shootees?
3. Post the ballistic gelatin wound profile of WWII 6.5 Jap ball ammo?