Too Much and Too Wrong Powder!!!
The 6,5 X50SR T38, was developed at an early stage of Nitro Powder Development.
Before WWI, most Rifle Powders were Fast, Hot and Erosive. By WWI, Powders had developed to " cooler", and slower Burning, more adapted to Rifle use.
Replacing the early ",Type B" powder, by the newer " "Type S" before the 1920s, this was a Powder similar to Dupont's later IMR 3031.
Long use over 40 years in Handloading by myself ( from 1967, first T38 Carbine, and using #3031, gave proper Velocities, accuracy, and recoil with 139gn Flat Base ( == original T38 Bullet).
Powder density at 30-32 grains fills case to bullet Base without crushing ( important).
Any slower powder, such as 4831, which requires heavier loads, is a bomb waiting to happen. The T38 is a very strong sction, but nothing can defeat Stupid.
The only other powder good for 6,5 Arisaka is IMR 4895, or its equivalent, Hodgdon 4895 ( Aussie AR2206H), again 30-32 grains, Max 34.
Good safe Load, PPU cases ( Norma are incorrect SAAMI undersized. Remember Japanese chambers are " relieved" to facilitate Chambering AND Extraction in Battle Conditions ( Mud, Blood and Beer).
Doc AV
Reloading Monitor.