So in nutshell, you cannot own any auto weapon made after 1986? That is stupid!
No, it's diabolical and ingenious. The government knows that some day there will be no more machine guns, or too expensive for anyone to shoot. Also, by forcing people who like machine guns to shoot old, beat up full-auto weapons is like handing them a grenade that will eventually go off and destroy the machine-gun loving owner.
It may take 50 or 300 years. Would you do mag dumps in a 150 year old Ruger AC556?