You might want to see if the gun is registered before tossing it. Sometimes, paperwork gets lost, there is a M2 up for auction on one of the NFA sites for about 6000.00 If it isn't on the registry you can cut up the receiver and still use the stock/barrel etc. and toss the F/A parts out. Just my .02, some folks will say, you should just ditch the weapon and run, which is perfectly OK as well.
Sometimes, it pays to do some digging, My co-worker came into a F/A rifle this way, it was his father's found in a safe after his passing, no paperwork was found with it, consequently the first thought was that this was an illegal rifle. Being prudent, he made an inquiry to BATFE, and found out that it was indeed registered to his father. All his guns had been willed to his only son (my co worker) and once things went through probate, it was x-fered to him, WITHOUT him paying an additional 200 dollars to transfer the weapon to him.