[medalguy]

Since an AR-15 is manufactured to fire semi and cannot be made to fire full auto without some machine work on the lower receiver to allow the full auto parts to be placed in the gun, why is possession of the auto parts a violation? The AR-15 does not fire automatically and cannot be readily converted to fire full auto.

This is not like the M1 carbine where you can simply replace some parts and have a functioning machine gun. There's quite a bit of machine work required.