The truth is that all semi-automatic firearms can be bump fired, even without bump stock attachments. No extraneous equipment is necessary, if you know how to do it. And YouTube is full of instructional videos, showing how to bump fire even semi-automatic pistols as though they were machine guns. https://www.thenation.com/article/society/court-finds-bump-stocks-legal/
No one wants to confront that reality, though, because it would mean acknowledging that the vast majority of guns in circulation in America can fire this way, right off the shelf and with no accessories, and we’d just be stuck with a ruling that says, “Well, we don’t know what to do because they’re just too popular”