If one character used the Avada Kedavra against an armed wizard (has his wand on the ready), can that armed wizard use the same curse curse to block Avada Kedavra? I know Avada Kedavra is considered "unblockable", but assuming that it is the same spell, I wonder if both curses would just nullify each other, if they are cast will the same amount of intent and power.

If one character used the Avada Kedavra against an armed wizard (has his wand on the ready), can that armed wizard use the same curse to block Avada Kedavra? I know Avada Kedavra is considered "unblockable", but assuming that it is the same spell, I wonder if both curses would just nullify each other, if they are cast will the same amount of intent and power.