If its upgraded,the bullet if touching wall (except alive entities like vehicles,players and everything but not walls)instead of just hitting it, the sides of the bullet will little "broke" causing splash damage around the bullet
If its launcher-like or plasma guns it will not work,only for pistols,rifles,shotguns and snipers,instead it will bigger 0.3x splash damage caused by launcher-like and plasma guns.
With the alive entities it will act like a normal bullet if its not launcher-like and plasma guns,if its hit by them,no boost to the normal splash damage will be.