Alright, I am going to give you constructive criticism.
Now, the title says that it is supposed to be a machinegun bunker, so I'll revolve around that.
I am guessing that the blue thing on the top is the machinegun.
First, the machinegun needs to look like an actual machine gun. I can't really describe what it looks like right now. Also, the bowl shape thing I am assuming is the bunker. You might want to make it sandbags or identifiably concrete.
You need to add shading so it doesn't look flat. You should make the bottom wider than the top, also.
