What exactly does offensive piercing do with missiles?

[aceface]

I don't see any point in using piercing over explosive with missiles. What is the difference?

 

[Aynslei]

Based on the changes I would assume that they do more damage to the hp of a block while ignoring a portion of the armor the block may have. IE I think they will kill armor blocks better.
Though I am not certain since I know things work differently on missiles.