The Concealed-Carry Fantasy

[gejohnston]

62. easy

Let's say that tomorrow, a practical, reliable gun were developed that (along with its ammo) was totally invisible to security scanners.

Theoretically, already illegal to have in the US. However, that does not prevent the vast majority of gun makers from making them, only exporting them to the US. Assassins and terrorist would take advantage of the train station loophole, like the Charlie Hebdo killers got their machine guns.
http://www.telegraph.co.uk/news/worldnews/europe/france/11818920/French-train-attack-Belgian-station-is-close-to-notorious-weapons-supply-line.html

Or... what if some micro-ammunition was invented that would let handgun carriers go about with 1,000 lethal rounds in one clip?

Yes.

Or... what if some sort of ammo (rocket-assist?) were invented that would be effective through six inches of concrete?

I think it would be a destructive device under the National Firearms Act.

All covered by 2A?

Just like websites.

(And before you say how ridiculous these examples are, compare a 9 mm. automatic with a high-capacity magazine to a musket.)

Yet repeating weapons existed and were not that unusual at the time.