Hi all! Looking for some help and advice here please?

Machine: Star SX-38 Type A
Material: AMS5659 / 15-5PH Stainless steel

Operation: Balance turning, going from 12.7mm (stock) to 5.1mm dia. Rough turn frm turret taking it down to 7.1mm dia, leading by 0.5mm. Finish turn from Path 1 Platten tool to finish size.

Speeds + Feeds: 2500 rpm, 0.1 mm/rev.

Inserts: Rough turn = Sandvik DCMT 04MF 2025. Finish turn = Sumitomo DCMT 04N-SU AC630M

Problem: Getting a total runout of around 0.1-0.2 in the centre of the shaft between centres. Runout drops to around 0.05 at either end of the shaft.

I have tried a couple of different insert grades, I have tried enabling constant suface speed maxing out at 4500rpm, at this point I am suspecting material stress/shrinkage while turning, but I'm not sure if there are any recommendations for solving this.