How is a gun a 'tool'?

[Tiberius]

A common trait among the pro-gun crowd is to refer to a gun as a 'tool', as if they are no different from hammers or socket wrenches. In light of the nature of this debate, it seems intentionally misleading to do this.

I don't think I've ever heard a pro-gun person compare a gun to a hammer or a socket wrench. I think that comparison exists only in your mind.

The dictionary does not seem to provide a single example, other than the first (which is vague and can apply to pretty much anything) which accurately describes a gun.

Not sure how "a handheld device that aids in accomplishing a task" can apply to pretty much anything. It doesn't apply to cars, windows, roads, etc. Have you considered that the definition is vague because "tool" is a very generic description of something? When describing a gun, my first word wouldn't be "tool", but that does not mean it isn't one.

I think of a tool as an object used in the repair or construction of something else, as most people do. What does one build or repair with guns?

If you think of a tool as an object used in repair / construction, then it is you who are in the wrong here, as clearly evidenced by the dictionary definition you cited.