Batman Shoots Superman kryptonite bullet
A green kryptonite bullet can neutralize both a Kryptonian's invulnerability and their healing factor. This makes bullets a potent weapon against Kryptonians; if a green kryptonite bullet is not removed soon after a Kryptonian is shot, it can potentially kill him or her.
In Lois and Clark, a green Kryptonite bullet is also used to bring Superman back in control when his powers become over-amped by red Kryptonite and a sample of Kryptonite was used to starve out a Kryptonian virus Superman was introduced to by Mrs. Church.
Green Kryptonite appears in the direct to video movie, Justice League: Doom. In the film, Metallo nearly kills Superman by shooting him the chest with a bullet made of Green Kryptonite, sending him falling from the roof of the Daily Planet and onto the pavement below. Superman's Kryptonian skin prevents the paramedics at the scene from removing the bullet, but he is ultimately saved after Cyborg uses a makeshift Kryptonite laser to cut an incision in the hero's chest, allowing Martian Manhunter to remove the Kryptonite before it kills him.
I'm sure there are other instances of kryptonite bullets, but mostly it's just a handy way of getting the krpytonite to him. Frankly though, superman is unlikely to be killed off so we won't see a kryptonite bullet used successfully on him.