As written here:
Liberals have one anti-gun argument that they seem to bring up just about any time they find themselves in a debate over 2nd Amendment rights, and sadly, a lot of conservatives don’t know how to counter it. That’s part of the reason why liberals love it so much!
The argument is this: the Founding Fathers drafted the Bill of Rights during a time when the only real firepower available was single shot rifles with bayonets on them. So if they wrote the 2nd Amendment with these kinds of guns in mind, they would’ve never had the poor judgement to make the same rights apply to scary rifles that can fire more than one round at a time.
There’s more there, but distilled down to its essence is this(I put the links in-line):
If you haven’t seen it before, this is possibly the most important rifle in U.S. History.
This is an air rifle that fires .46 caliber balls and was taken on the Lewis & Clark expedition. Dr. Beeman’s vetting of the rifle as belonging to Meriwether Lewis is long, but worth a read.
The Girandoni rifle was standardized for the Austrian Army in 1780, nine years before the Second Amendment was ratified. It held 20 rounds and could fire all of them in less than a minute. It was effective on whitetail deer, which means it could be effective against two-legged targets as well.
This, along with the Belton flintlock, smashes to pieces the notion that somehow the founders of our great nation spoke only of smoothbore muskets when penning the second amendment and could not conceive of high-capacity rapid-fire weapons.