Hi it depends what rifle stock, wood or aluminum. Wood stocks are usually 5nm. The aluminum stock may requier some experimenting. Start by marking the possition of the screws then loosen the screw, and as you tighten with a torque wrench notice what torque value brings it back to the original screw possition. I hope this helps you out.
Kiwi Bob,
About 5.5 to 6.5 Nm was best depending on ammo (Eley Match EPS). I have heard of people using down to 4Nm). Depends on where you have the front O-ring/damper set. Try it at 20mm to start with
Cheers
Martin