It's a bullet but I'm not sure what type, calling it a maxi or mini
"ball"
seems like an odd name for it.

Not sure about a "Maxi" ball, but a "Minnie" (not "mini" ball is
named after the inventor. A projectile used in the Civil war era to
replace the previous bullets, which were round balls. The term "ball"
continued for some time after that, even applying to 38 special revolver
cartridges and 45 ACP cartridges during WWII. The Minnie ball (it
really needs an accent somewhere which I am not prepared to add) had a
hollow base. It was easily slid down on top of the power with the
ramrod, and when fired, it expanded to grip the rifling more firmly.

I had already suggested a bullet with a Minnie ball as a
possibility, and the way to tell is to look at the bottom. If it is
flat, it was a more recent cast lead bullet. If it has a significant
cavity in the base, it is more likely to be a Minnie ball, though I
believe that the outer surface is normally smoothly curved, not stepped
as this one is.


Thanks for the information, I'll have to do some research on this one. I
added another photo showing the bottom, it is hollow and about 1/2" deep:

http://puzzlephotos.blogspot.com/