Dave Kopel has an excellent article over at the WaPo detailing the fact that the Founding Fathers could have indeed envisioned repeating firearms, because there were several examples of them that were contemporaneous with the founding, or predated it. Even Henry VIII had a long gun that used a revolving cylinder to fire multiple shots without reloading. The issue was not that repeating firearms were unknown, it’s that they had to be hand made and were therefore the province of the very wealthy.
I’ve never believed that any of the founders would be supporters of modern gun control, mostly because they were gun enthusiasts themselves. There’s always the temptation on the other side to try to channel the founding to their own ends, but the fact is at the time, civilian ownership of firearms was wholly uncontroversial.