I want when my bullet entity collides with a wall to place decal on the hit vertex. I tried many ways, but I can't make it work. Here is the function where the decal placing code must be added. help pls

function remove_bullets() // this function runs when the bullet collides with something
{
wait (1);
//here must be the decal placing code
ent_remove (my); // and then remove the bullet
}