What is the story and why lord Ram want to kill Hanuman and finally used Brahmastra but failed? How could the Brahmastra failed?
I'm not export to answer these kind of question but will try to post here, what i read and watched in Movies.
There were two ways of explanation for this question.
2-> RAM Nama is powerful Than RAMA himself Proved by Narada muni
astras in this world will kill Hanuman, not only Brahmastra, Even Loard Shiva's Pashupathastra, Loard Vishnu Sudharshan Chagra etc