Both Karna and Drona were capable of using Brahmastra while battling Ghatotkacha.
Drona didn't use brahmastra and in the end Karna used the Divine Weapon that can be used only One Time against Ghatotkacha which was given by Lord Indra.
QUESTION :
- Why Both Drona and Karna didn't kill Ghatotkacha by using Brahmastra ?