It was the earlier Arisakas in 6.5mm. I thought P.O. Ackley conducted these tests while working at the Springfield Armory as part of military testing? (Or where they done later in his career?) I know the 7.7 Japanese was adopted in 1939 in the Model 99 Arisaka, though both it and the 6.5 Japanese continuted to see use throughout the war.
Gosh, you' ve got me on this one! I was always under the impression that P.O. did these tests when he was in business for himself AFTER WWII, but it could very well have been when he was working for the Ordnance Department during the war! I do know he used barrels chambered for the .270 Ackley Magnum in the Arisaka blowup tests, and all he could do was to blow the barrel off in front of the receiver ring! After which, he could unscrew the barrel stub, rebarrel the action, and go on shooting! He never succeeded in destroying the Arisaka action. No other bolt-action would stand up to this abuse.