Why shouldn't anybody know it? Do an FOIA and see what kind of ammo they buy. No big deal. The first time that I saw the idea of them using prefragmented rounds (like magsafe) was on the TV show "Crossing Jordan". Pretty silly, really, but they were trying to maintain the "explosive decompression" myth that hollywood has been exploiting for years.
The thing is that if you were to remove an entire window from the airplane at 30,000 feet, the air system of the aircraft would still be able to keep up with pressure loss. It's not that big of a deal. There is no reason to carry special ammunition for use on an airplane.
Some police departments carry silvertips. Some carry hydrashocks. Some carry golden sabers. Some carry semi-wadcutters. It's not that big of a deal.