Full project at my repo.
Again built from reference images before listening to instruction on how to do it. The body of my gun was made from one cube. I did horizontal loop cut; bezel for width; extraction and size the loop across the bottom. I then did a vertical loop cut for that indention. I selected the faces to move in, extracted and sized it. I had to merge some vertices and remove one face where the indents meet. I also used an array to get the 3 guns vs linked objects. I find that more efficient as long as I am not planning to resize any of them in object mode. I also though the barrel went into a recess on the cannon instead of a flush mounting on the front.
