Factor in deceleration? It's about 1.93 seconds. But still not near 7. Maybe to hear the sound bounce back if hitting a plate(do 77 grain bullets make a sound loud enough to hear at 1000 yards?)
My 1.5 second estimate wasn't entirely off the cuff. My 75gr bullet at a very pedestrian 2788fps is 1.57 seconds (bottom right). I let AB do the heavy lifting on the math so I didnt hurt myself