There is a magazine limit of 10 rounds. Owning or buying a magazine with a larger round capacity is illegal.
Some states have a limit on the number of rounds a magazine can hold. In these states purchasing, selling, or transferring a magazine of larger size than the law allows is a crime. In some cases magazines that were bought before the law was put in place must be registered with the police, in others they may only be loaded to the number of rounds legal in a state. The law may vary in some cities.