Peep sights have been around since Roman times (on cross bows) and there is at least one documented case of a flintlock rifle with a telescopic sight during the American Revolution (cooperative effort between a telescope maker and a gunsmith). So peep sights may not be common, but they could certainly have been used on anything that fired a projectile or aligned any type of sighting instrument (sextant, alidade, astrolabe, telescope, etc.) for the last couple of thousand years.