It sez "Keep and Bear ..... that means "carry"..... that would be a sensible, defensible limit.
That definition would mean that limits could be placed on the ownership of a Cival War era canon, since it is too heavy to be carried by a man... But that ownership of an advanced MANPADS could not be limited, or infringed, by the government.... MANPADS = man portable air defense systems, i.e. shoulder launched surface to air missiles. At least 7 commercial jet airliners have been attacked with MANPADS by terrorists in the last 40 years.