dnd 5e – Does the Spell Sniper feat double the range of booming blade when you are not wielding a reach weapon?

The range of the spell doubles, but trivially so.

The first bullet of Spell Sniper says:

When you cast a spell that requires you to make an attack roll, the spell’s range is doubled.

This answer goes into detail about the interaction between Spell Sniper and booming blade. The short verion is, as Rubiksmoose writes:

Spell sniper will work because booming blade has an attack roll involved in it as long as you have a weapon capable of making a melee attack.

So it technically doubles the range of the spell, but this adjustment is entirely trivial without a reach weapon: with a reach of 5 feet, you can still only make an attack on a creature within 5 feet. Booming blade doesn’t extend the reach of your non-reach weapon, but the range of the spell is technically 10 feet with spell sniper, though it still fails if you do not make a melee attack against a creature (or cannot).

Unless you are a bugbear!

The bugbear playable race has a feature called Long-Limbed:

When you make a melee attack on your turn, your reach for it is 5 feet greater than normal.

So even with a non-reach weapon, Spell Sniper would enable the bugbear to use booming blade on targets 10 feet away. In this case, it’s actually very important to understand that the range of the spell is actually doubled.