+p and +p+ are 'hotter' rounds. In simple terms +p means its got more powder, and +p+ would mean even more. More powder means a faster round, but it also means alot more pressure on the round. Some firearms are not rated for shooting +p ammo. I would check with Ruger C.S. to assure the blackhawk is safe to shoot +p
http://www.saami.org/specifications_and_information/publications/download/205.pdf
http://en.wikipedia.org/wiki/SAAMI
http://www.saami.org/specifications_and_information/publications/download/205.pdf
http://en.wikipedia.org/wiki/SAAMI