Sir Joseph Whitworth is quite the famous name in engineering circles, credited with the development of such things as Whitworth threading (the first standardized thread pattern) and engineer’s blue. When he decided to make a rifle, he decided that he could make flat surfaces more precisely than round ones, and chose to design a rifle with a hexagonal bore and mechanically fitted bullets.
Video: [15:19]
https://youtu.be/Hi-S_horZGk?si=
Ian makes a correction to the original video: [7:18]
https://youtu.be/cUd2RQGfL7E?si=
Spinning “rifling” is what makes a bullet go straight. Before then, you’d just have to hope it hits in that general area you’re aiming for. Any imbalance in weight would steer the bullet then.