By the time Bryshon Nellum graduated from Long Beach Poly High in Long Beach, Calif., as the 2007 national track and field athlete of the year, he had already circled 2012 as the best chance to make his first real run at the Olympics. Several bullet wounds and several surgeries later, the USC senior sprinter is right on track. Nellum had the fastest qualifying time in the quarter-mile race during the Pac-12 Track & Field Championships Saturday, doing so just 3 1/2 years after a shotgun blast hit his legs and left his future on the track in doubt. “It feels great,” Nellum said after running 45.98 seconds in his 400 heat. “I can’t even really explain it. Man, it’s just unexplainable.