300mgs per week of Test E will produce gains if the diet and training program are in order especially if its his or your first cycle, 300mg is around the threshold for building muscle tissue so i cant see why you cant or your friend cant. If the base as been built from yrs of training and you have reach a natural limit your body should be ready to grow and 300-500 per wk will be fine if its a first cycle and everything else is in place.
How long has he been training and how old is he?