How does a guided bullet work? I always thought that was one of those perpetually ten years away kind of things.
http://bulletin.accurateshooter.com/2018/07/guided-50-calibe...
https://www.darpa.mil/news-events/2015-04-27
Sandia National Laboratories did something similar, but with a non-standard rifle and using a laser target designator. Russia is attempting to do something similar.
Many years ago I saw a concept of a guided machine gun bullet in a "scientific" magazine; the concept involved steering by a mechanism that moved a lump of mass within the bullet around.
Of course that could all be a lie to throw adversaries off the scent, but the trouble with trying to keep a bullet top-secret is the moment you use it, the enemy has as many as they want to study...