There are questions that are about weapons, but are not about guns, for example:
Has weather been weaponised? ,
Would a laser weapon visibly fire? ,
Do hovercraft trigger minefields? ,
Does the use of tasers by the police lead to an increase in people killed by police? ,
and others which means that weapons must remain.
However, there are many questions that are tagged as guns but without the weapons tag, or quastions about guns that are tagged only as weapons. Which means that if a user searches for a question about guns, they will not find all the relevant questions, and the same goes for weapons. In a world where all the users tag their question perfectly, questions about guns would be tagged as both guns and as weapons.
But since this isn't the case, and in order to avoid bad tagging, I'm for unifying both tags under weapons, and add a note in the description that the tag is for all types of weapons including firearms and guns.