Your civil war Enfield minie-bullet is a Confederate-made cast-lead one which accidentally contained an airbubble trapped inside the lead when the bullet was being cast in a bulletmold. When your minie-bullet was fired, the firing-blast blew through the thin lead around the airbubble, resulting in what civil war bullet-collectors call a "blow-through" minie.
The first photo below shows a cut-in-half minie with two small airbubbles trapped inside it. I suspect that it the case with the one you found, due to having a blow-hole in its nose AND in its side.
The airbubble inside yours was fairly small, which produced a non-catastrophic blow-through. A large airbubble results in what you see in the other photo below.
This is probably the weirdest shot bullet I have found.I am not sure how to measure bullet's ,but it is the size of a 58 minie,it is hollow all the way through,and looks to have a blowout spot on its side.I am hoping maybe some kind of explosive bullet.Sorry about some of the blurry picture's.Camera died and I have no batteries at this time
