I see that totw has 2 different types. Can anyone enlighten me as to the difference?
One is historically correct for the Civil War.
The other has a thicker skirt and more bearing surface for heavier loads and better accuracy.
Only the improved version is offered in calibers other than .58 since a caliber other than .58 would not be historically correct for Civil War era Minié in the first place.
The Maxi-Ball is a Thompson Center design that does not feature a hollow base.
The original Minié design actually had an iron wedge that was driven into the base of the bullet by the powder gasses to expand the bullet into the rifling, then it was quickly discovered that a hollow base by itself was enough.
Then TC found out that the base does not really even need to be hollow with their Maxi-Balls, the pressure, if high enough, will still expand the base of the bullet into the rifling. Pure lead is soft enough to distort under that much pressure.
This may also be responsible for the fact that patched round balls lose accuracy with really light loads.
I have a .45 Maxi-Ball mold and I have found that accuracy is so-so until near maximum loads, then all of a sudden, they become tack drivers. They also work quite well in my Ruger Old Army revolver.