Need help/comment from expert out there...

My company is developing gun drilling on a CNC Swiss type with high pressure coolant pump 120 bar (max). We are using gun drill from TIEFBOHRTECHNIK GmbH. The Gun drill size is Ø2.48mm with kidney bean-shaped coolant hole, using vegetable based coolant vascomill10, material is SUS 17-4 (Ø1/2 inch) and the hole depth is 100mm.

Pilot Hole - Ø2.485mm with 4mm depth.
Gun drill - Feed into pilot hole with turn the spindle speed on 600 RPM, when achieve depth 3.5mm, turn on the high pressure coolant and increase the spindle RPM step by step till 6500 RPM.
Drilling Method - Pecking 5mm each 25mm depth.

Hole Requirement.
- Concentricity max 0.10mm

Defects.
- Concentricity more than 0.10mm (max 0.18) on and off. Best achievable 0.020mm
- 50% reject rate.

I feel that the coolant pressure is too low.


Any help/comments are appreciated.
Thanks!