600 rounds per minute, times 6 or 8 guns, spraying how many pounds of lead per second?
They're not all going to hit the pilot. They're going to shotgun blast everything in the cockpit.
Not all are in the front of the cockpit, and even so, you're not going to get multiple planes in one pass. The navigator was usually towards the rear of the cockpit, which, unlike the fighters, are quite large. Plus, even if you don't know how to fly it well, I'm sure a gunner could take control of the plane, bombadier etc... etc...
The point is, you'd have to kill the crew, not just one man to send the bomber spiraling downwards, and even so, you'd still not be able to get multiple bombers in one pass, you'd be hard pressed IRL to even get one in one pass.