You do realize that all the steroids in the world are only going to do 'so much' with a terrible muscle-building diet plan, right? Besides, any gains you get you'll lose if you don't start eating to support them. The most common cause of not gaining weight? Not eating enough to support muscle growth, plain and simple.
I don't mean to sound harsh but by reading your statements it's clear that you really have no idea about these steroid precursors. They are NOT FOR YOU.
I'd imagine as a swimmer you want to stay quite lean, right? There's ways to bulk up and gain a bit of extra at along with the muscle, and there's way to minimize fat gain (this way is, of course, longer and tougher).
Anyway, set a 6-8 meal per day diet full of clean, healthy calories and monitor protein/carb/fat (PCF) intake daily. Eat the same exact things every day if you have to (I set my diet as per my goals at the time and eat the same damn thing every day until it all needs tweaking) and you'll gain. You don't even need supplements . They have their place but realize they are SUPPLEMENTAL to a proper diet. Without that, you've got nothing. Most gains obtained will be lost due to improper nutrition shortly after. that's why everyone goes around saying 'yea, (such-n-such) works but i lost all my gains once i stopped it.' Reason? Not eating to support it. It's all in the diet, end of story, no questions. Ask any bodybuilder in the world the importance of diet and you'll see what I mean.
To figure what amount of calories you'll need, understand BMR. Basal Metabolic Rate is the amount of calories your body uses up just 'being'. Do the math: BMR = 66 + (13.7 x weight in kg) + (5 x height in cm) - (6.8 x age). 20% above that is primo for putting on lean weight (whereas 20% less would be a good starting point to maintain muscle mass and shed fat - again, in both, a proper diet of
natural foods is key).
...or say "screw that" and take chemicals which you don't understand and **** yourself up.

No one likes to do things the hard (and safe) way. I guarantee you if you dose ProMagnon all the way through without proper post cycle therapy (yes, it does have steroid properties) to get your test levels kicking again, you are going to be quite displeased with the effects it has on your body. Namely estrogen production among possible others. Trust me. That's not to say you can't BE safe using steroids, precursors, or anything of the like, but you have to KNOW what you're doing. Not understanding that this compound IS of steroidal nature, you simply don't come off as knowing what you're doing.
Now of course, what I suggested isn't the only way to gain muscle. There's people who put on muscle more easily than others, and other variables that help/hinder. BUT if the there's a quicker/better/safe way as a general rule to build muscle other than with a finely-tuned diet, the entire world's bodybuilding community would like to hear it
FWIW I'm not going to monitor this thread as I don't want to get sucked into this vs. that with everybody (everyone always wants to). If YOU personally want my help, PM me and I will help.