If you are in the military, you'll have mags issued to you.  It is legal for the unit to own restricted mags, but NOT legal for an individual soldier to own his own restricted mags.  In other words, they would only be legal if they were issued to you, and you would be required to turn them in.  These days, magazines are tracked pretty tightly in the military, which is very different than how it used to be.

-Troy