Specifies a decal and impact by surface type (on projectile blueprint)

hi guys i need help .
i want to specifies a decal and impact by surface type (on projectile blueprint).
it works on the character BP.
but i want to make it in the projectile BP.
as u can see i put a print string to what the phys mat return.
and it every time return Default witch is the first surface type in my project.
while i have 20.
i got this message errors too .
as u can see there is somthing wronge on breakhitresuolt_physmat.
i dont know what but .
i think i should do something in the constructor (maybe).
(this is the character BP and the projectile BP http://s15.postimg.org/ntk5efdqz/mycharacter.png