and civilian AK lookalikes, and those features are the only significant ways in which an AR-15 or non-automatic civilian AK differ from a self-loading, detachable-magazine hunting rifle like a Remington 7400 or a Ruger Mini Thirty.
So they came up with a features list and defined an "assault weapon" as a civilian detachable-magazine rifle that had an arbitrary number of features (the 1994 Feinstein law allowed one listed feature per rifle, and banned new rifles with two or more). They did come up with some rather creative
post facto justifications for banning features (such as the idea that a protruding handgrip optimizes the rifle for firing from the hip, or that an adjustable stock would make a rifle easier to conceal on the person) in order to justify the features list, but the original reason was to try to figure out a statuatory way to distinguish modern-looking rifles from traditional-looking rifles.
Of course, this didn't ban AR's and AK's at all, since the only feature difficult to remove is the protruding handgrip (because of the way the receiver is shaped); manufacturers switched to smooth muzzles (or pin-on brakes, since muzzle threads were the listed feature) and deleted bayonet lugs so the protruding handgrip would be the only listed feature. Here's my ban-era civilian AK (2002 model) with altered areas circled:
and of course the hysteria surrounding them drove sales through the roof.
Later "expanded" AWB proposals (e.g., H.R.1022
et seq) would reduce the number of allowed "evil features" to zero, so that new-production rifles can't look so much like AK's. Of course, this doesn't really work either, because you can always refit a civilian AK with a straight 19th-century-style stock and move the trigger guard slightly to the rear:
and have an AK that is absolutely identical in every definable way to a Ruger or Remington (which functionally it already is). So some of the newer proposals also ban rifles by design heritage, i.e. if a civilian rifle is derived from a police or military design, it is an "assault weapon," regardless of features or function.
One final image, of my Ruger Mini-14 Ranch Rifle (that I owned from 1989 to 2006-ish):
Same rifle, 3 different stocks. With the first and second stocks, it was listed by name in the 1994 Feinstein AWB as "particularly suitable for sporting purposes" (zero and one listed feature, respectively), but putting the third stock on the rifle would have been illegal since it would have resulted in two listed features (protruding handgrip and a folding stock). The California AWB bans it with the second stock, but not the first stock. S.1431/H.R.2038/H.R.1022
et seq would ban it with the first stock, by name. So you can see the arbitrary aspect; it depends on who is writing the legislation and what they like and dislike, IMO.