First, how the Brady Gun Ban people wanted to define 'arsenal':
Section 204 -Prohibits a person from possessing more than 20 firearms or more than 1,000 rounds of ammunition unless the person is a licensed dealer or has been issued an arsenal license. Direct the Secretary of the Treasury to issue such a license if specified conditions are met, including the payment of a $300 fee for a three-year license period. Subjects the holder of such a license to all requirements pertaining to licensed dealers. Sets penalties for violations.
Followed by, as the definition of a 'firearm',
So, if you had three actual guns, and three magazines each, and a few boxes of ammo; or just a couple of boxes of ammo and some spare parts- extractors, ejector, springs- you have an 'arsenal' and would require a license. Or if you have a couple of .22 rifles and two bricks of ammo. A license for which the requirements and cost could be jacked up constantly to cause people to give up. On top of that, just think of all the crap that has been used by bad agents at BATFE to screw over dealers being used on you("You don't have these magazines stored properly, that'll cost you your license! And you'll be lucky if you don't face charges!").
SEC. 312. DEFINITION OF FIREARM EXPANDED TO INCLUDE COMPONENT PARTS.
Section 921(a)(3)(B) of title 18, United States Code, is amended by
striking "or receiver" and inserting ", receiver, barrel, stock, ammunition
magazine, or any part of the action".
And if there's any question in your mind what the Brady Gun-Ban group actually wants,
I'm convinced that we have to have federal legislation to build on. We're going to have to take one step at a time, and the first step is necessarily — given the political realities — going to be very modest. Of course, it's true that politicians will then go home and say, "This is a great law. The problem is solved." And it's also true that such statements will tend to defuse the gun-control issue for a time. So then we'll have to strengthen that law, and then again to strengthen that law, and maybe again and again. Right now, though, we'd be satisfied not with half a loaf but with a slice. Our ultimate goal — total control of handguns in the United States — is going to take time. My estimate is from seven to ten years. The problem is to slow down the increasing number of handguns sold in this country. The second problem is to get them all registered. And the final problem is to make the possession of all handguns and all handgun ammunition — except for the military, policemen, licensed security guards, licensed sporting clubs, and licensed gun collectors — totally illegal.
Thanks to Thirdpower for pointing to these quotes.