SOOOOOOOOOOO sorry! Is there any way you can get the bullet? My cat was shot about six years ago and I also found him on the porch, unable to move. We got him to the Vet and the bullet had broken his pelvis. Fortunately he survived and is fine now, but the bullet is still inside his body! The x-ray shows that it is from some kind of canister air gun. I tried to find out who in our neighborhood had one of those guns, but was unable to find out.
I'm so sorry about what happened. People can be so cruel.