Maybe I missed it in the rules, but does it state anywhere how you count ammo expenditure? Is it based on RoF, how many possible hits you can make, how many actual hits you make, or what? Unless I missed it, this seems like a pretty humorous oversight. I've seen some other mentions of references to pinning and other rules that have been taken out.
Could this be an opportunity to throw out a mechanic that most people don't seem to follow/one that adds more book-keeping? Could it somehow be tied to a combination of degrees of success/failure and RoF?