Okay, strictly speaking an arsenal is defined as either a collection of guns, or a place to store guns. (I looked it up). So I guess, technically, three or four guns could be called an arsenal, but the way it's traditionally been used, that just ain't right, and it makes possessing a few gun sound more dangerous.
After all, why would ANYONE need more than ONE gun? One gun will do everything.
While I don't have any illegal weapons . . . as a matter of fact, I don't even have any "black" guns -- don't own a single synthetic stocked or polymer framed firearm, I'm a steel and wood type of guy -- if news crew looked in my basement it would definitely be "film at 11" time. I have more than four.