it is a small point, but jon does have a real issue with the collector thing. perhaps there should be a separate collector's license which requires that none of the weapons or munitions purchased under that license can ever be discharged or used.
There are currently two ways in which a legitimate "collector" can legally possess military-grade weapons. Federal Curio and Relic License, and a Class III Federal Firearms License.
The C&R License requires the weapon in question to be at least 50 years old, to be in unmodified form, etc. It requires a full background check, certification of safe storage, and costs about $300. It does NOT allow possession of fully automatic weapons.
The Class III FFL (which is actually designed for dealers, manufacturers, etc, but is available for individual collectors), requires a very lengthy background check, federal inspection and certification of high-security storage, etc, and costs $3000. This DOES permit ownership of fully-automatic weapons.
In other words, there is no actual reason why an individual can't own a machine gun under current laws - as long as they comply with the requirements of a Class III license. If for some reason you want to play collector of an arsenal of fully-automatic rifles, all you need is a license and a lot of cash.