Without requiring an NFA permit, the largest bore weapon a civilian can own is .50 calibre/12.7 millimetre in the US. Anything with a larger bore requires an NFA Destructive Device permit.
The classification of the bazooka as a small arm is a bit questionable. Although it was carried by an individual, it was served by a gunner and loader/ammo bearer, which made it a crew served weapon. Small arms are individual weapons.
In some countries which field it, it's operated as a crew served weapon. However, in the US military, it is fielded as an individual weapon.
The biggest, newest, most powerful weapon on this planet is my brain after answering certain sorts of questions.
No because it is a weapon
Anyone who can legally possess one.
The BATFE web site has all the pertinent information.
Shakuhachi
The nuclear bomb.
Krupps works at Essen in Germany .
Depends on whether you're doing it legally or not.
How can a weapon NOT BE a weapon? Chemical gas attacks, various "automatic" weapons, machine /gatlin guns etc. The biggest weapon. not a weapon in the sense of a single person activating it was the introduction, by the British, of the tank.
It caused high civilian casualties but did not result in surrender. Tokyo was firebombed before the US decided to use the first nuclear weapon against a city containing civilians.