Daystate mk3 figure 8 clamp
Thinking about what Holy said,does your rifle have a figure 8 barrel cylinder clamp?
I know nothing about the mk3's but if it does have a clamp i would loosen the grub screw's and let thing's centralise then retighten.
The S400 are well known for shifting when the barrel get's knocked hard and that's a result of the clamp.
If it does not have a clamp then you should be fine with your re-zero.
See you Sunday
About as much use at field target , as a life guard at the Olympic swimming pool.