Without trying to undermine your own work too much, this is what I came up with about 2 months back, unfortunately, I never textured it, "colouring in" isn't one of better abilities... I think the barrel looks a little long, but it was also modelled in front of an image, so I'll assume it's right, and I'll also assume that we didn't use the same image
I must repeat, this is not intended to put your work down (personally, I don't think I'm really in any position without a texture), I'm merely pointing out why I think yours has a bit of a wonky barrel...