Sorry, but I do not believe you gained 55lbs of muscle, if you are truly natural.
According to Blood and Guts, by 1996, after 10 years of training (and heavy doping) Dorian Yates gained 70lbs of muscle.
I also do not like naturals who go around left and right feeling the need to scream out the fact that they are natural. Show humility and be the best you can be. I am a natural and love bodybuilding for what is it, and appreciate the hard work that TRUE bodybuilders put in, drugs or no drugs. Dorian Yates without drugs would have been just as diligent, determined, and hard-working as Dorian with drugs. In fact, he stated that he wished bodybuilding was without the drugs as the sport would receive more recognition.
Now, on a side note, what is your diet like, and your training as well.
Yeah, it would be unrealistic to gain 50lbs of muscle or more without drugs....after consistent training for some years. Try training for a few years, then eating very little, quit lifting all together, start back with a crazy diet and routine, with zero deviations. Many people out there have lost 80lbs of fat, why can't you gain 40-60lbs of muscle...over some time. I've been consitent for 5 years now, but the first year back I put on 50lbs, probably 15lbs fat? Even 35lbs of muscle in a year seems a bit much, but with some muscle memory and a radical change in calorie intake, it's not all that impossible.
Whether or not your believe that, is irrelevant to how I've made my gains.
Here's the thing about most bodybuilders who juice, most juicers simply can't do much without drugs...plain and simple. Sure, some have a strong base to build off of, but very few I'd say. It's basically a crutch. And the whole competing thing is grand and all, but usually just an excuse to blast more juice and give it some bigger purpose than what it really is...drug abuse, nothing more. You can paint it any shade you want, it is how it is.