Im guessing that bull is dead somewhere and that it could be likely you got both lungs. Grid the area and keep looking if you have the time. That broad head could have hit the far shoulder and bounced back like said before, with the pounds you shoot and weight of those arrows I would think you would blow through a rib. I shot a spike this year and hit a rib square on...it busted that rib in two and still was a complete pass through @ 40 yards. Good luck on what sounds like a great bull.