You know how a train has angled wheels on each side so any perturbation will naturally cause the wheels to turn back towards the center? It's kind of like that. A perturbation away from the center causes a force to return towards the center but it's not damped all the way so there's a persistent wave motion back and forth at a characteristic frequency.
A bullet is like that but has more degrees of freedom so there are a few of these kinematic modes happening at the same time.
I don’t know why but that just gave me a whole new perspective on what’s happening in flight. I had been thinking of the visually perceptible motion but that made me think of the forces at play while it’s basically in freefall spinning in a slippery pocket of air.
Everything happens so fast it’s easy to forget that physics is still happening one molecule at a time.
A bullet is like that but has more degrees of freedom so there are a few of these kinematic modes happening at the same time.