I use Blender. My tip for you is the same as Dark Souls. Get Gud.
Sorry, but I'm no expert at it even though it is my "go to" for designing. I sucked at it until I sucked at it a little less, and so on.
I started by watching videos. Then I did a "follow along design", noting everything that was done (I think I made a tie fighter then a coffee mug).
Then I started converting PDO files. After getting comfortable with that, I started converting game assets. If I want more detail, I add it myself so long as it is within reason.
Dash, You got any other pics of that(one from head on, top down, bottom up maybe)? Does it go over the muzzle of the DMR? If so, what's the diameter of the muzzle you have?