So intrinsically we can imagine the bullet (a cluster of particles) moving through a medium (a sea of particles), and as the cluster moves, it bumps into lots of particles within the sea and imparts some kinetic energy to each of the sea's particles as the cluster moves through the sea. As the kinetic energy is moved outside of the cluster, the cluster slows down.
My question is: Could we imagine the air immediately in front of the bullet as having a higher pressure than the rest of the air, thus slowing the bullet? Or could we also imagine the air behind the bullet as being more vacuum-like than the rest of the air? This pressure difference between the front and back of the bullet would explain why the bullet slows down. Or is the only actual answer that of, the air particles gliding over the bullet are "scraping" away some of the kinetic energy?
I guess my question may be getting a little theoretical, but I've been obsessing over this for a bit now and I just can't talk myself into one reasoning or the other as to why the bullet slows down.