very nive toy :) great model. very nicely detailed. your shaders could take some improvements. i think (based on that reference photo) you have made the metals slightly too metallic, and the rest a bit flat. maybe you should boost your diffuse a bit more and lower specularity in some parts?
Good stuff. A few crits though: There are a lot of unneeded loops on the receiver for the low poly. It could really be optimized a lot more. There are also a lot of frontal details modeled in on the low poly that will never be seen on a first person weapon. The spec is making the gun look cloudy. I'd try and limit the…