tapwater,
I don't know when your son went through basic, but currently the training course including qualification is a total of 80 rounds. Breaks down into 16 rounds to get zeroed in, 24 rounds of practice, and 40 rounds for qualification. Ranges are 75, 175, and 300 meters (simulated by using scaled down targets on a 25 yard range).
Granted, that doesn't sound like a lot but if you don't qualify, you'll end up firing whatever it takes you to get good enough to qualify, and if you do qualify, you don't need to fire more, right?
Just a Shooter (and proud son of a retired USAF Chief Master Sergeant)