Won't this depend a lot on the altitude?

Also, if the plane is traveling at 1466 m/s it will cover 4984m in 3.4s. So that's about 1.25 bullets for every linear meter of travel (6248 rounds), but we have to account for the width of the targeted area which would depend on the spread at the distance from the muzzle (dependent on the altitude). Let's assume it's a strip 5km long by 10m wide for simplicity... and we're looking at like 1 bullet for every 8 square meters... that's going to be mostly miss. If the infantry have any cover at all it's going to be a very futile exercise.

You'd probably be better off dropping hand grenades out of the plane than dealing with that ridiculous contraption.

Also worth noting that flying low enough to be in effective range for the mounted firearms means that the plane will be in effective range for firearms... which is not really where you want to be in a ~~bomber~~ giant target. I wouldn't want to fly this mission.