Yeah, none of them seem to be aware of guns. You now how often dark wizards do spells in the books to protect themselves against projectiles? Never. They never do a spell like that, so far as I know.
As far as I know, the Protego spell protects against physical forces. The reason no one uses projectiles (they certainly could catapult stuff around with spells as well) is probably because it's common knowledge that it does nothing.
Boring? This is the same universe where wizards canonically defecated in the streets and used fecal vanishing spells.
However, when Hogwarts’ plumbing became more elaborate in the eighteenth century (this was a rare instance of wizards copying Muggles, because hitherto they simply relieved themselves wherever they stood, and vanished the evidence), the entrance to the Chamber was threatened, being located on the site of a proposed bathroom.