Ovality of turned parts

Good Morning,
I am turning 303 grade stainless steel from 4 mm dia to 3.175 (g6), I am measuring the dia with a 0-25 mic and am getting ovality of 4 to 5 microns, I am able to keep in the tol limits but does anyone have any suggestions please, I am using a 5c collet and chuck to grip the bar

Thanks

Nigel