Is this your first attempt at LDD guns? Not bad. It does need work, though. It kinda reminds me of those old school revolvers. The kind where you had to break it open like a double barrel shotgun to reload it. I don't really use gray pieces when I do my guns. They have a much better selection of black. Keep working at it.
It can use some improvement, but it's a good start. I've been around revolvers, so I have a good understanding of them. First, for a multi-barrel revolver (as opposed to single shot) the cylinder should be larger. The pistol grip is usually done differently (see pics of revolver via image search) and the hammer usually curves more and is thinner. I myself have yet to try building one, so I can't giv specific suggestions yet. Good luck! BTW: check out and review my guns!