What is the difference in a civil war bullet from the confederacy and the union?

Even though both sides used the same rifles, their bullets were slightly different in how they were made. The muzzle-loading rifles used a Minie ball that was a conical bullet with a hollow base. The outside of the base had rings molded into them by the bullet mold.

In general the difference was the number of grooves at the base: 2 or 3. I forget which side had which number: believe the Confederate used the 2 grooves. Also, some of the Confederate bullets were made very crudely and some have been found that were more blunt with no grooves at all.