I just took my son shooting today. I have a 1931 Mexican Mauser chambered in 7x57. We used Federal "Blue Box" ammunition. When I came home I thought I would try to see if an AAA or AA battery would fit in the shell holder from the box. The AA didn't fit at all. The larger hole for the cartridge body is too large for the AAA. But, the smaller one that the bullet/projectile goes in holds the AAA very snugly. I could cut away what isn't needed. Since my camera went on the fritz I'm afraid I can't post a picture.