Before going to Calibris with Donna Noble, the Doctor encountered Time Reaver guns several times. On one occasion he saw someone being preserved in time until they changed their will. On another, he saw a mother continually shooting her son to keep him from leaving home.
When the Vacintians found out that their sun was dying, they decided to use Time Reaver guns en masse to extend their lives. However, Cora stole several guns and tried to sell them on Calibris, believing that others could use them for good. (AUDIO: Time Reaver)