Copper and lead are actually magnetic — more accurately, they’re diamagnetic. Thus, in theory, a magnetic field in front of the copper-jacketed lead bullet could resist the bullet’s motion and, along with a field around it, suspend it in the air.
image/text credit: NightHawkInLight
Cusick attempted to slow down or stop a magnetic cannonball by shooting it through electromagnetic induced force fields in copper.This video tests a question: can induced magnetic fields in copper stop a magnetic bullet?
In reality, the strength of a magnetic field capable of stopping a supersonic bullet1 at point-blank range is astronomically staggering, and would have all kinds of effects on ferromagnetic materials all around.
Someone better at the math than I could probably tell you how much energy would be required to bring a typical magnetic bullet to rest from a velocity of at least 360m/s in the space of no more than half a meter. Even one strong enough to suspend a bullet in mid-air is mind-boggling.