small trick i found

[melodicmizery]

i was doing a no herb run on normal and got to the urias boss with chris. well the area for running is shit, the bomb detonator is slow, and his reload is even slower on his gun. i then realized i was a noob and frusterated with normal i did this

backed all my saves up
switched game to easy (there is a autosave before you jump in the cave)
beat the game on easy using no herbs. trophy popped, challenge popped

went back to my cloud download only the autosave. this kept my challenge unlocked
kept playing on normal using herbs this time. alot easier. 

my first run was on easy and i didnt realize how much they bump up the difficulty on normal. should of did my no herb run on easy. and then i realized i was a noob

anyways that might help someone if they are stuck in the similar scenario as me