Rmplstlskn, if it is a legal Form 1/4 MG, then get the forms and get it in your name. The price of MGs is going up everyday. MACs cost between $1000 and $1500 for a legal transferrable plus the $200 tax. One destroyed transferrable = one less transferrable out there.
If you are in the Lauderdale area, email me and I can explain what the Mag Well is, etc... I am not familiar with the fire controls on a MAC. So, if anybody has diagrams please email me a copy.
If you can't find the Form 1/4, you could contact the ATF (Pay Phone of course) and see if they can find it in their DB. But, considering the lack of maintanance of the DB, they might not find it even if it were legal. If they can't find it, you are SOL and would have to turn the Receiver over to the ATF.
Your other options, albeit illegal are to either --
a) Keep the gun and risk going to prison.
b) Find a water tight box and an anchor. Place the receiver in the water tight box and securly attach the anchor to the box. Take it 3+ miles out to sea on the Atlantic Side or 10+ miles on the Gulf Side and drop the box and anchor. Log the position with a GPS on a map and head home. If the laws ever change (Amnesty ???), you could go back and get your Receiver. You could also go back any time you wish, bring it up and shoot it. Of course, you'd want to make sure the water isn't more than say 90 feet deep so that you could dive down and get it. This option assumes of course you have access to a boat and SCUBA Equipment and know how to use them properly.