Originally posted by: Neutral2
Karn get Brahmastra from Parsurama.
Dhritrastra asked Sanjay-
As regards Karna, how, indeed, could Death touch him, that
hero equal unto Indra himself, while he was engaged in shooting his manifold celestial weapons? He unto whom in exchange for his earrings, Purandara had given that foe slaying, gold-decked, and celestial dart of the splendour of lightning,"he who had, lying (within his quiver) amid sandal-dust, that snakemouthed celestial arrow decked with gold, equipped with goodly wings, and capable of slaying all foes, he who, disregarding those heroic and mighty car-warriors having Bhishma and Drona at their head, had acquired from Jamadagni's son the terrible brahmastra, that mighty-armed one,
Even yudi also know Brahmastra from Drona. Thats why Karna asked for Brahmastra.
Drona teach Arjun about Brahmashira after Drupad war.
It is possible that Karn went to Parsurama after defeat in Drupad war.
It is also possible that Drupad may have use brahmastra. How could Karn with Kavach Kundal lost to Drupad???