Get Ackley's book, Handbook for Shoooters and Reloaders, and he goes into why the action was so strong. Since the 7.7 was 311 caliber, it could be rechambered to 06 case, but would have to use 303 bullets. I've heard the story too about the 6.5, but it was a shorter round and not sure the action would take an 06 case.
Today, there are a LOT of stronger actions than the Arisaka's. The Rem. 700 about the strongest action out there. In a blow up test in the 40s, when the 721 first came out, Gen. Hatcher and his folks blew up a number of other actions, but were unable to blow the 721. The charge they had in it, to get to bulging and locking up the action, was a case FULL of proof powder, with a 180gr bullet, and then 5 or so MORE 180gr bullets, shoved down the barrel on top of it. What happens in most blow ups is, the case is not entirely supported, some of it, like in the model 70, is not supported, do to the design of the action. The pressures in the cartridge then let the unsupported area BLOW away, and feed gasses, etc., through the action, which destroys it. With the head of the cartridge being totally surrounded by steel, as in the 721-700 action, there is no unsupported case head area.
The Rem 700 is definately not stronger than the Arissaka. The Rem-700 has .020" unsupported case. Surrounding the case head with steel is not needed, since the case head is the streoingest part of the case
