Well, the true definition of a Minie ball is the three rings (but depending on the manufacturer, this could be 1, 2, or 3), but, it needs to have a hollow base. And upon this, the Minie ball is only a musket round, which means that it would be .577 in diameter. Because there diameter, and as stated above, it is a carbine bullet.
But out of curiosity, where did you find them, on what battle, and can you guess what side?
Edit: And I am not an expert in carbine bullets, but remember, it too is lead, so you have to know that the measurement you have right now is going to be a tad less because there is about 150 years of crap sticking to it.