The artillery bombardment was not the largest or longest in the world. Some of the WWI pre-assault bombardments lasted days and involved thousands of artillery pieces. the largest in the new world, yes it was the largest.
In the spring of 1863, the fuse factory in Richmond blew up.
Confederate Ordnance ordered the arsenal at Selma AL. to ramp up production to supply the ANV with case fuses. The Selma fuses would fly about 200 yards further then the Richmond fuses when cut to the same length. Lee nor Pendelton were not informed of the change in fuse supply.
The Confederate artillerymen would have had a pretty good idea of the range to the Union front line. That range would have been used to set the case fuses for the bombardment.
Once the first volley was fired gun smoke would have obscured the view of Union lines. Almost no wind that day so the gun smoke just stayed close to the ground hiding the view of the target.
Course I meant largest and longest bombardment up until that time. You can’t judge the past by the future. I don’t think the length of fuse has anything to do with the length of trajectory of the ball. If the ball lands where is supposed to the fact that it blows up 15 seconds later it’s not nearly as big a deal as missing the target by 100 yards.