jwall,

Actually, Eleanor O'Connor chose the 7x57. Jack had one made for himself, but after Eleanor shot it she essentially said, "This one's mine." Jack eventually got another one built, which he used extensively toward the end of his life.

The cartridge he actually chose for Eleanor was the .257 Roberts, when they were living in Arizona. But she evidently wanted a little more zap when they moved to Idaho and could hunt elk every year.

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck