If that is powder in the base of the bullet it isn't from an"exploding" bullet. It could be unburned powder residue that went down range with the bullet. The base of the bullet is hollow so it can expand when it is fired and fill the barrel sealing off the gases behind it. It improves velocity and accuracy albeit not too much accuracy in an unrifled muzzle loader. Lack of accuracy is why the early troops fired in volleys. If enough bullets went down range they were bound to hit something. Rarely is all the powder burned so it would be perfectly normal for unburned powder or residue to be inside the hollow base.
As for what page, I just looked for two ring bullets over .60 caliber and with hollow bases and couldn't ID any specific one for sure so I didn't make a note of the page number. If you have the book look through it and you will see what I mean. The two horizontal marks look like deformed rings to me and just gave me a hint as to what they might be, I don't think you will ever be able to narrow it down to a specific bullet or gun because of the deformation, but will just have to make an educated guess and that's what I have done.I have personally fired thousands of rounds of all types of bullets including many different muzzle loading ones as well as solid lead handgun bullets and this is the best guess I can make. Now the bullet could be one that has never been fired at all and for whatever reason just got deformed either accidentally or purposly. I think it would take a detailed forensic examination to determine that. Therefore I am just guessing. Take it or leave it, just tryiing to help. Monty