Just make sure your property insurance company knows the value of your machine gun. Document it, pay the small "rider" fee that they will charge, and if it ever gets destroyed, insist they reimburse you market value. Even if you are talking about a Mac10, machine guns are more expensive and harder to find then regular guns, and you should make sure your policy will cover them.
(Also for the foil hatters - how much arm twisting would it take for an Administration to get insured firearms lists from insurance companies? )
I don't think anyone should be too worried about Obama or any other administration getting a hold of a list of NFA firearms from insurance companies when he can strut right in and get the info from the DOJ.
This is pretty much the route you'll have to go... Have a rider to cover full market replacement value (+ stamp, if they'll let you). Check the going prices ever quarter or so and update the policy as needed.
As much as I don't like letting an insurance company know that I own a machine gun (which I don't...) = should something happen to it in a home disaster, I'd rather be covered for the $5k - 50k replacement values.
(Also for the foil hatters - how much arm twisting would it take for an Administration to get insured firearms lists from insurance companies? )
-J-
What they dont know wont hurt them.