I just test fired a new Ruger Blackhawk in 45 Colt today. First round fired ruptured the cylinder and split the the next case. Bullet was 250 gr. cast, lubed, and gaschecked. Powder was 7.1 gr. of Winchester 231. According to my load books that is a light load. Any ideas about what would have caused this? Fortunately, no one was hurt.