A device designed to kill massive amounts of humans in very short time is called ...

[Thor_MN]

17. If you want to use something as an argument, it is on you to provide a link.

Something like this:https://en.wikipedia.org/wiki/Girandoni_air_rifle

The rifle was 4 ft (1.2 m) long and weighed 10 lb (4.5 kg), about the same basic size and weight as other muskets of the time. It fired a .46 caliber ball [3] (caliber is contested, original sources such as Dolleczek [4] describe the caliber as 13mm (.51cal)) and it had a tubular, gravity-fed magazine with a capacity of 20 balls. This gravity operated design was such that the rifle had to be pointed upwards in order to drop each ball into the breech block. Unlike its contemporary, muzzle-loading muskets, which required the rifleman to stand up to reload with powder and ball, the shooter could reload a ball from the magazine by holding the rifle vertically while lying on his back and operating the ball delivery mechanism. The rifleman then could roll back into position to fire, allowing the rifleman to keep a "low profile".

Regardless of anything else, it is clearly not a semi-automatic, which fires with each trigger pull. A semi-automatic requires nothing other than a trigger pull to fire subsequent rounds. The authors of the Bill of Rights did not know of any weapons that could fire with just another trigger pull.

If you were talking about :

You defeat your own argument. The rifle has to be vertical to reload. Clearly, the design goes along with the concepts of the day, that muzzle loading guns need to be vertical to reload. They could. with a simple design change, allow the weapon to be reloaded without pointing it to the sky, but the concept DID NOT exist at the time. The authors of the Bill of Rights knew nothing of semi-automatic weapons.