Good stuff dude. I'd recommend breaking up the smooth surfaces (like the wheels and cannon) by adding a few bumps'n'dents... kinda like the metal-rings on the barrel. It doesn't make sense that the texture conveys such a worn-off surface but the actual surface (conveyed by the highlight) remains perfectly smooth.
You should think about toning the spec down on your barrel. make it 1/4th as shiny as it is now. I would also bring the glossiness down as well. Good rule of thumb: Surfaces that are 100% smooth have the highest amount of gloss, because they reflect light perfectly. This is why polished marble reflects light so well --…