It's been ruled constitutional for those states to ban:
(1) Large‐capacity magazines (holding more than ten rounds).
(2) Semiautomatic assault weapons (whatever that means).
However, the portion of the New York law which made it illegal to load more than seven rounds into a ten round magazine was judged to be unconstitutionally stupid. I paraphrase, the actual words the court used were "does not survive intermediate scrutiny in the absence of requisite record evidence and a substantial relationship between the statutory provision and important state safety interests."
The New York legislature originally considered imposing a seven round magazine limit, however when it was pointed out that magazines weren't generally made for semiautomatic rifles in that capacity, they "graciously" allowed ten round magazines so long as they weren't loaded with more than seven bullets, except in a firing range or official shooting competition where I guess you could still legally load the full ten. The court found the obvious problem:
"New York has failed to present evidence that the mere existence of this load limit will convince any would‐be malefactors to load magazines capable of holding ten rounds with only the permissible seven."It's good to read that, as one of the one of problems with calls for common-sense gun controls is that many of the proposals lack common sense, and usually courts won't get into that kind of second-guessing.
And what is a semiautomatic assault weapon? In Connecticut's case the list of features that turn an otherwise legal gun model into an assault weapon include a telescoping stock, a thumbhole stock, a forward pistol grip, a flash suppressor, a grenade launcher, and a threaded barrel capable of accepting a flash suppressor or silencer. In other words, you can have a semiautomatic rifle in Connecticut with a ten round magazine so long as it doesn't have any of those other features. I can't think of a single mass shooter in the U.S. who has used a grenade launcher.
The assault weapon feature list in New York also included a bayonet mount. I'd much rather have a Sandy Hook type shooter try to bayonet me with his assault weapon than spray me with bullets. He'd have to get in close, and I might be able to lodge that bayonet into a wall or car or tree effectively rendering his weapon unusable. But I digress.
The court-accepted rationale is that assault weapons, however defined, are unusually dangerous:
At least since the enactment of the federal assault‐weapons ban, semiautomatic assault weapons have been understood to pose unusual risks. When used, these weapons tend to result in more numerous wounds, more serious wounds, and more victims. These weapons are disproportionately used in crime, and particularly in criminal mass shootings like the attack in Newtown. They are also disproportionately used to kill law enforcement officers: one study shows that between 1998 and 2001, assault weapons were used to gun down at least twenty percent of officers killed in the line of duty.The gun rights advocates tried to argue that the assault weapon term was either unconstitutionally vague or unconstitutionally banned a whole class of weapons. The court essentially said they couldn't have it both ways, if it was a class it couldn't be vague. Here's the rub:
In both states, citizens may continue to arm themselves with non-semiautomatic weapons or with any semiautomatic gun that does not contain any of the enumerated military‐style features. Similarly, while citizens may not acquire high‐capacity magazines, they can purchase any number of magazines with a capacity of ten or fewer rounds. In sum, numerous "alternatives remain for law‐abiding citizens to acquire a firearm for self‐defense." We agree with the D.C. Circuit that "the prohibition of semi‐automatic rifles and large-capacity magazines does not effectively disarm individuals or substantially affect their ability to defend themselves." The burden imposed by the challenged legislation is real, but it is not "severe."The court concluded that the statutes "impinge upon Second Amendment rights" but ultimately did not find that they "infringe." So will this go to the U.S. Supreme Court? My cynical guess is that it probably will not, because the gun rights side probably lacks the confidence it would win and fears setting a nationwide precedent. Nonetheless, the precedent is set and it's up to each state to decide whether it wants to set these limits.