Tau weapon. Can't get a proper circle on the weapon I'm trying to obtain a perfect circular shape. On the right I'm just adding 2 edges around the middle, but it gives me an imperfectly circular shape, where I am trying to obtain a result equal to the one on the left. It is perfectly rounded but that will change when I do the same thing, as I did on the right.

Any ideas on how to fix this issue?
Two methods. Method 1 is to make the two elements comprising the weapon as separate meshes neither of which affects the other.  Method 2 is to create Tse circular mesh, and choose two points on the circumference from which to extrude the horizontal element.