Unless your a genetic freak,
It is close to impossible for the human body to synthesize more than
1.25-1.5 pounds of muscle per week. W/O assistance!!
This condition assumes a nearly close to perfect anabolic state.
Which is only possible for newer trainees.
1.5 x 12 weeks = 18 pounds best case scenario.
That being said, I would still love to see you do it.
keep us informed
Good Luck
M.D