Semi-automatic assault weapons, large ammunition clips & lack of background checks are the physical & moral equivalent of yelling fire in a crowded theater, inciting people to riot, libel, slander & obscenity, all of which are “speech” of a sort that isn't protected by the 1st Amendment. This type of “speech” can be prohibited or regulated even though that Amendment says “Congress shall make no law .... abridging the freedom of speech”.
Those who say that no law or regulations can be passed affecting the manufacture, sale or ownership of weapons due to the protections of the 2nd Amendment fail to realize that all parts of the Constitution are subject reasonable and common sense interpretation and limitations just like the 1st Amendment is, as described above.