There is NO way to defend ownership of this kind of military gun,
It would indeed be more difficult to defend opposition to the assault weapon bans if the object of the ban was military grade weaponry. Unfortunately for you, assault weapons are not "military grade" weapons, they are "military style" weapons. Modern military battle rifles are fully automatic -- select fire weapons capable of firing more than one round with each pull of the trigger. Assualt weapons are incapable of full auto-- select fire operation and will fire only one round at a time. No modern military force employs or even would want to employ these "assault weapons" as their main battle rifle as they are not nearly as capable and deadly as the full auto-- select fire rifles employed.
Instead, "assault weapons" are designed for the civilian market and are functionally equivalent to many other quite legal firearms... the only distinction being some cosmetic features which make them LOOOK like a military grade weapon.... sorta like painting a racing stripe on your Hyundai and thinking that you now have a NASCAR race car capable of winning the Daytona 500. You will be disheartend when you find out the Hyundai with the racing stripe still has the same engine and does not have a chance at Daytona... But it still looks faster!