Actually, some parts look pretty good to me, I don't know if everything hes trying to draw is perfectly cylindrical.
Maybe a picture of some reference would help.
That said, the scope is definitely cylindrical, and it looks pretty flat. The problem is the shading ( mostly ). Take a look at this reference:
There is also a problem with the barrel, esp at the end where it has some detail that appears to wrap around, it looks more like a straight band.