fburtgx: I don't know myself - I was NOT there and have never owned a 50 caliber BMG type Rifle.
I wonder if the bullet started out at say 2,000 F.P.S. and probably slowed down a LOT maybe averaging 1,132 F.P.S. over that 11,319 feet.
Thus that is how whoever wrote the story came up with that 10 second figure.
The VERY informative link that "AJ300MAG" linked to above shows a chart that alludes to the bullet getting there (travelling the 11,319 feet!) in just under 10 seconds.
I guess we could figure out the exact time if we knew the Ballistic Coefficient, weight and muzzle velocity off that 50 BMG round?
I will check into this a bit.
Hold into the wind
VarmintGuy