Check this video:
Here you can see a true power of pbr-rendering in q2xp engine. Take a look at machinegun, there are 2 different materials - glossy edges and opaque main metal. Its hard to setup, but looks great and the pipeline is similar to Unreal Engine 4 rendering.
And another feature - muzzle flash for machinegun. The original game don't have such feature, but you asked about this, so we made it!
If you like my models - please, support me at: