Hey, that is indeed looking strange! I think I can help with the turret though, my guess is that it’s either inside an object that’s hidden in the viewport but not hidden from the render (check the eye and camera icons in the outliner – not sure if you have any objects below the camera) or the normals for it are inside out.
For the seam in the middle, double check that there is not an interior face there if you turn the mirror modifier off.
If that doesn’t help, upload your file to pasteall.org or dropbox and I can take a look! It could very well be a beta bug, as I can’t think of anything that would cause that type of banding.
