Alright, using the texture name method, I found out it was hitting the floor of the level (the entity is a bullet, by the way). So I did what Logan said, but for some reason it still didn't work. I found it was still hitting the floor, so I then made the code this:
c_trace(vector(my.x,my.y,my.z),vec_rotate(vector(my.x+5,my.y,my.z),my.pan),IGNORE_ME|IGNORE_YOU);
This actually somewhat works. I guess the c_trace was coming from the origin of the entity, and just pointing at the floor. So I changed the 5,0,0 vector to that, and it then started working. But, now the c_trace seems a bit screwy. Sometimes the bullets don't activate the c_trace and slide along the wall, sometimes they make each other disappear, and sometimes they disappear before they should (too far away from the walls). I assume I changed the 5,0,0 to the wrong thing, so it's doing something very weird at the moment.
So since the c_trace was going from the entity down to the floor, what should I change the c_trace code to?