Would normally mean a hand made hollow point-like bullet. Made by filing a groove, drilling a hole or any other modification to a normal bullet to cause it to mushroom or shatter on impact with a body. The term comes from the British colonization of India, they had an arsenal at Dum Dum where they were "invented". They were eventually made "illegal" by most armies and in some armies merely possessing dum dums was a hanging offense.
I suspect in this case it may be a vernacular term for hollow points as opposed to the hand made variety.
This is correct, except the bullet was in fact a .303 british rifle round that was NOT a soft point nor was it Cut in any way shape or form nor was it a Hollow point. It was in fact a solid tip projectile that got a stupid name because of the factory where they were made. People over the years have come up with the idea that any type of projectile that is a soft tip a hollow point or that has been scored in any way type or fashion is then a Dum Dum projectile. NOT SO.
Whatever they are the Doctor said they disintegrated and disappeared in the victims' bodies. Pretty slick, the magic disappearing bullet! I bet Carolyn McCarthy is writing legislation to ban them right now.