Elendil's Sword and Sauron's Ring

Originally Posted by Encaitare

Narsil was probably stronger than the average sword, but I suppose Sauron was not entirely immune to being wounded anyway.

So it is likely that the One Ring gave Sauron greater strength but not invulnerability perhaps. What about the WK - could Narsil break his immunity spell? There is no record that I know of as to whether Narsil was magical (i.e. it was not an elven blade). So how can this sword harm Sauron, but most probably not the WK or Gandalf?