It should be based on firing mechanism, barrel size, and round type: all firearms with 1)semi-automatic firing, plus either 2a)barrels larger than a pistol barrel or 2b)high-powered rifle type ammunition should be classified as Assault Weapons in my view. So everything in the AR family and adjacent, basically, but nothing else. If you do it properly on a technical basis, the whole issue about labels is solved.
(Handguns with semi-automatic firing would NOT be covered by the ban I’m describing - that’s a separate issue.)
Just to give a flavor, here is subsection a) of the CA law (it goes all the way to e) if you want to read it):
(a) Notwithstanding Section 30510, “assault weapon” also means any of the following:
(1) A semiautomatic, centerfire rifle that does not have a fixed magazine but has any one of the following:
(A) A pistol grip that protrudes conspicuously beneath the action of the weapon.
(B) A thumbhole stock.
© A folding or telescoping stock.
(D) A grenade launcher or flare launcher.
(E) A flash suppressor.
(F) A forward pistol grip.
(2) A semiautomatic, centerfire rifle that has a fixed magazine with the capacity to accept more than 10 rounds.
(3) A semiautomatic, centerfire rifle that has an overall length of less than 30 inches.
(4) A semiautomatic pistol that does not have a fixed magazine but has any one of the following:
(A) A threaded barrel, capable of accepting a flash suppressor, forward handgrip, or silencer.
(B) A second handgrip.
© A shroud that is attached to, or partially or completely encircles, the barrel that allows the bearer to fire the weapon without burning the bearer’s hand, except a slide that encloses the barrel.
(D) The capacity to accept a detachable magazine at some location outside of the pistol grip.
(5) A semiautomatic pistol with a fixed magazine that has the capacity to accept more than 10 rounds.
(6) A semiautomatic shotgun that has both of the following:
(A) A folding or telescoping stock.
(B) A pistol grip that protrudes conspicuously beneath the action of the weapon, thumbhole stock, or vertical handgrip.
(7) A semiautomatic shotgun that does not have a fixed magazine.
(8) Any shotgun with a revolving cylinder.
(9) A semiautomatic centerfire firearm that is not a rifle, pistol, or shotgun, that does not have a fixed magazine, but that has any one of the following:
(A) A pistol grip that protrudes conspicuously beneath the action of the weapon.
(B) A thumbhole stock.
© A folding or telescoping stock.
(D) A grenade launcher or flare launcher.
(E) A flash suppressor.
(F) A forward pistol grip.
(G) A threaded barrel, capable of accepting a flash suppressor, forward handgrip, or silencer.
(H) A second handgrip.
(I) A shroud that is attached to, or partially or completely encircles, the barrel that allows the bearer to fire the weapon without burning the bearer’s hand, except a slide that encloses the barrel.
(J) The capacity to accept a detachable magazine at some location outside of the pistol grip.
(10) A semiautomatic centerfire firearm that is not a rifle, pistol, or shotgun, that has a fixed magazine with the capacity to accept more than 10 rounds.
(11) A semiautomatic centerfire firearm that is not a rifle, pistol, or shotgun, that has an overall length of less than 30 inches.