Hey everyone, I'm new here been looking into a Martin recurve for quite some time now, found a seller online selling a used Martin mamba but it's all black instead of the brown and black I see on the site, From photos sent to me the info I can get on the bow is

50#@28
HM 0402
Amo 58

Any idea on how old this bow might be? Also how much harder is a 50 lb bow to pull compared to a 35lb ive been shooting a 35lb bow for over a year now and its gotten to the point where it feels like im pulling almost nothing, I don't really have access to a shop where I can try other bows and I also don't have to money to buy multiple bows, any help would be much appreciated thanks in advance