http://blog.beretta.com/10-gun-tips-you-need-to-know-about-flying-with-guns
6. You can pack ammo in the same locking case.
This is another area that’s misunderstood and full of internet myth. Your ammo just needs to be stored in some type of safe container and not loose. Technically, you can keep ammunition in magazines, but I wouldn’t recommend it. It meets the letter of the law storage requirement, but too many airline and TSA agents will give you grief. Use a plastic ammo box or original cardboard packaging and you’ll be fine carrying that in the same lockable case as your gun.