A gun is defined by the dictionary as a weapon incorporating a metal tube from which bullets, shells, or other missiles are propelled by explosive force, typically making a characteristic loud, sharp noise. The purpose of a gun is as bellow;
if I am been plain and without been bias –is to kill something someone. It's an instrument that has enough power, when used properly (and most times improperly) to kill. Hunting rifles and shotguns are for killing animals which can be used for wild reserve. ... But guns are only for killing.

A Bomb is a anything filled with explosive materials or incendiary material, designed to explode on impact or when detonated by a timing, proximity, or remote-control device.

Looking at the definition above it's human to provide solutions to human need which this two instruments has great solutions too and also it's also a source of income to the manufacturer who must have seen business opportunity in it's production.