No, that's not what I was saying. The ammunition in question is proper 7.7x58 Arisaka. Your gun has been rechambered for .30-06.
Will .30-06 fit in the magazine? If it does the gun has had some proper work done to it. If only the chamber is modified you have a bolt action single shot.
I'd have the headspacing checked to be sure everything's okay for that round. The 'smith should also stamp the appropriate chambering information on the barrel while he's at it.
7.7x58 is a shorter round than '06. Because of the long bullet jump there wasn't a whole lot of pressure needed to get the bullet out of the case. After that, there wasn't a whole lot of pressure difference between the inside and outside of the case since you didn't get a good seal at the neck. One brand of case was harder that the other and didn't stretch as much.
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