I'm an Army officer and hear that the Air Force has almost zero weapons training. If you want to learn to use weapons, go into Army or Marine infantry units. Even regular Army infantry won't satisfy the real gun fan. You'll get some, but never enough, training. In the regular Army, I rarely was given the opportunity to fire my M4, and it was almost always a miserable experience (strict range rules, full body armor and kevlar helmet, etc.).
For Army, you may even want to go one further into the Special Operations units. It is there that you will really get great training opportunities. It wasn't until I was in a SF unit that I was afforded the best and most relaxed weapons training.