Are Brahmin bugged atm? When I was level 2 or 3 I killed plenty, just north of NCR, with a DE.44 pistol.
But for tor the last two evenings, and I am now level 6, I hit them with my new hand-crafted DE.44 and it always does 0 damage. Even crits to the eyes. I do not have any problem with scorpions, little geckos, mole rats etc.
*JHP ammo in both cases.