Not to continue beating a dead horse, but I gained 8 lbs of what I thought was muscle in 5 weeks when I first started lifting weights.
I don't have a chemistry background and I can't tell you precisely what I did. But I started using whey protein for the first time, lifted heavy weights and ate more (all while also running more).
I was 16 and went from 6'0" 170 to 6'0" 178 in 5 weeks. I remember the amount because I was young and dumb and thought I could get to 190 by the start of school. I didn't. But that first month the weight was flying on.
Note, I probably added more calories than the recommended amount and it could easily have been aided by water weight, I don't know. But I know I got into better shape, increased cardio and gained 8 lbs in 5 weeks.