In 2013, the Colorado legislature passed House Bill 13-1224, to end the “sale, transfer, or possession of an ammunition feeding device that is capable of accepting, or that can be readily converted to accept, more than  rounds of ammunition or more than  shotgun shells (large-capacity magazine).” It was intended to erase the market for new large-capacity magazines.
Remember, this was a year after James Holmes used a semiautomatic rifle equipped with a 100-round drum magazine (among other weapons) to kill 12 people in a movie theater in Aurora, Colo.
The bill forbade new sales or transfers.
Fast forward to now. Sharp-eyed gun shops realized they hadn’t expressly forbidden “parts kits.” And that’s how large capacity magazines are now sold in Colorado. You buy a kit and put it together yourself.
Reason has a good piece on this here. There are a number of operations that don’t even bother making kits as they’re not abiding by the new law.
so, between exploitation and blatant disobedience of Colorado’s existing magazine ban, it doesn’t look like large-capacity magazines are going anywhere anytime soon in the Centennial State. In fact, Colorado’s Supreme Court heard arguments concerning the constitutionality of the state’s large-capacity magazine ban yesterday, meaning a repeal of this broken law is a possibility. Even if the ban doesn’t get overruled, as Reason‘s J.D. Tuccille notes, American gun owners’ usual response to arbitrary gun prohibition has been, “Molon labe,” or simply, “come and take them.”