Grinding

So I am an avid gamer with a particular liking to the Metal Gear Solid Franchise. Recently I have been playing the HD remake of Peace Walker and am trying to get all the trophies however this requires alot of grinding two missions over and over again to get a item drop. The drop and drop rate is completely random as I have done the mission over 100 times and yet my mate did it the same way and got it in 3. *sigh* so yea this is a pain in the neck and I'm loosing my sanity.

So TL:DR

MGS:PW is a pain in the flank to 100%