Live by the Gun....

I've been trying to figure out if I can gray scale with my copic markers. I only have three cool gray markers #7, 3, 1, gonna pic up more this weekend. Do you have advice on how to improve on this?

This was a very quick sketch (about 20 min, but i did try to gray scale it for like 1 hour lol) . These are concept characters, I'm still trying to get their look hammered out. Do you guys have any thoughts on them good or bad?