In the context of mass shoutings “assult riffle” refers to a gun capable of rapid fire. One in which the clip can be empty in seconds. Which is the type of gun used in almost every case  The semantics are generally only used by people who want no gun laws yet who also understand why the “not really an assault  riffle” gun is important in a war with other people and and better than pistols. Musket etc Anti gun people have one definition the milita has another. I mean even the marines and similar groups admit guns like a ar-15 are basically the same as any assist weapon they give you