mmm...hmmm..................
he has to be doin' like 4 spells at once. Gandalf needs one, and it's not really a spell.
He could just make something fall on Dumbledore.
Dumbledore wasn't even killed by a ring...He attempted to destroy a ring that belonged to a very powerful dark wizard (one that could own Gandalf himself) and it happened to injure him.
Which ring? The Ring of Fire? Pointless. The Horcrux? What would that accomplish? Dumbledore would just be like, "What is this shit, why are you showing me a retarded ring that I already cracked." Then he kills Gandalf.
Dumbledore wasn't even killed by a ring...He attempted to destroy a ring that belonged to a very powerful dark wizard (one that could own Gandalf himself) and it happened to injure him.