Not all cops are playing for money, this RP situation just makes 0 sense. The president walking around with an LMG just makes no sense at all. It would have been a little different if he had like 4 other players in suits with vests and stuff.
Last time I checked no matter the circumstances the president isn't going to be walking around carrying a LMG in real life, the secret service would (im guessing you were role playing as the president). In real life if someone was walking around with a gun such as the MK200 I guarantee you that they would be restrained. And if you wanted to RP it out you should have let him restrain you then RP it. I don't think any higher up would be in approval of letting someone walk around with an illegal gun such as that. You need to look at it from the cops view, he sees someone with a highly illegal weapon, his first reaction is going to be to restrain him to make sure that he is not a threat, he attempts to restrain you and you say "Im the president and the secret service gave me this for protection" and you blast him...