Life is stranger than fiction. We’ve all experienced moments in real life that would be considered bad, cheesy writing if we wrote them ourselves.

As far as “only effective over longer distances” is concerned, that’s just not a thing. Like, sure, I wouldn’t bring a hunting/sniper rifle to a close-quarters situation, and it would mean the overall setup would be pretty ineffective, but the weapon itself does not have an “effective minimum distance”.

There isn't a gun that works worse at close range.

This isn't Battlefield. Guns don't have a specific range where they're more deadly, in fact every bullet fired gets weaker over distance the moment it leaves the barrel. From there the thing that matters is projectile drag, barrel length, type of rifling, and the gunpowder load.

That type of gun is called a "rifle", and it's typically considered most effective at distances greater than ~3 feet. Any closer and you might need to step back to avoid smacking the target with the barrel.

Guns don't really have "effective ranges" like is often portrayed. Close range guns are usually close range because they're physically larger, not because of the movement of the bullet. A gun you need to point upwards to carry up stairs is not as good if you might need to fight on stairs. Likewise, if someone is close enough to grab the barrel you probably want a weapon that they can't do that to.
Weapons with longer barrels can often accelerate a bullet longer, giving it more power and accuracy. That's why they tend to be viewed as distance weapons.

One part practice, one part luck. Kirk was seated stock still had his attention fixed on his debate opponent, so this was probably an easier shot than the one that domed JFK, coming around a slow curve at Dealy Plaza.

A gun is just a tiny mechanical cannon. Explosives launch a bit of lead really really fast. Every gun does this, and I promise that lead doesn't care how far or close, if it gets you your gonna have a bad day.