Lately, "assault" weapons are (legally) characterized by the amount of ammo they can hold. For example this 30-round magazine is illegal no matter which gun you put it in, whereas the same gun with a different-sized magazine may well be legal. http://www.mediaite.com/online/nbcs-david-gregory-displays-3...
Magazine restrictions are a separate law in most states. California has an assault weapon ban which restricts features such a pistol grips, collapsible stocks, and flash hiders. They have another law restricting the possession of magazines with a capacity of more than 10 rounds. Old magazines are grandfathered in, so you can use them in legal rifles.
It looks like the law is similar in DC. Possession of a magazine with >10 round capacity is a crime. Other firearm laws are irrelevant to the case you linked to.
OK, interesting. I know my home state of NH also has an "assault weapons ban" that just bans certain magazines, although we probably have other laws too that one bugged me.
It looks like the law is similar in DC. Possession of a magazine with >10 round capacity is a crime. Other firearm laws are irrelevant to the case you linked to.