Sounds like someone pulled a bullet from a rifle barrel with one of those iron worms that were designed for that purpose, and the tool broke when they removed the ball. And then the ball was re-used with the iron fragment still embedded in it. Not an unlikely scenario in the heat of battle. And not necessarily an indication of anything "diabolical," although the whole concept of shooting at people with minie balls does indicate a complete lack of sensitivity on the part of the shooter.