Hey again,

I didn't see the option for "Keep faces together" in the extrude face option box. Here is a screenshot of the cannon, with the problem circled in red. In case you can't see what I did with the extrude face, I extruded a single face, scaled it down, and then extruded it inwards to make a tiny box. As you can see, it shines up the texture and, I'm assuming, makes it uneven.