King
One thing I have noticed that you have been doing is modelling the whole turret from one block - well it looks a bit like that so forgive me if I am wrong!
My approach to modelling has changed over the years and now I actually try an construct models like real-world items or in the case of tanks and planes like you would find in a plastic model kit.
For instance I would model the commander's copula separately, the gun mantle, the gun mantle plate and the top plate of the turret. This also allows you to add Subdivision Surfaces and edge loops to the models without making meshes too complex.
I hope that this makes sense. You model if progressing fine so far I would now just start breaking parts up then you can focus on these parts adding more detail. Keep chiseling away and comparing to what you have done and you will be amazed at the progress you are making.