I just received this response from the DC police:
The Metropolitan Police Department is in receipt of your e-mail regarding the David Gregory segment on "Meet the Press." MPD has received numerous e-mails informing us of the segment. NBC contacted MPD inquiring if they could utilize a high capacity magazine for their segment. NBC was informed that possession of a high capacity magazine is not permissible and their request was denied. This matter is currently being investigated. Thank you for taking the time to bring this matter to our attention.
Customer Service – Metropolitan Police Department