The concept is okay, a little short in my opinion. The idea of 2 bullets could be tweaked a little, mostly because I first thought that one gun fired penetrating bullets and the other explosive ones when I first read it and thought it had nothing to do with your actual semblance. BUT, here's what I was thinking that you may like and that works about the same way; Double-Tap, first hit marks the the victim with a target, hitting the same spot again would cause an explosion. One COULD be able to replicate your idea of semblance without having such semblance, while this ability is something of it's own that no one can replicate =J