The thing is, it's a whole lot harder to kill a whole bunch of people with a baseball bat than with an automatic rifle, or even with a handgun.

The kind of weapons they had back in the 18th Century were muzzle-loading pistols and single shot muskets and so forth. And swords of course. That's the kind of weaponry the people drawing up that amendment had in mind - so why take it any further and extend its range to cover all the other inconceivable weapons that have been dreamed up since?