Thanks for all the replies!

on a ten bull card I shoot them in a Z then a back to front Z (If that makes sense?). I'm shooting a Match 52 with a two stage trigger and Dioptre sights. I've been shooting for a good few years and this problem has only appeared in the last two months, no change of rifle or equipment.
I have made the trigger slightly heavier, shortened the travel on the first stage and moved the trigger further back and canted it over slightly so it sits naturally on the pad of my finger.
I'll see how it goes and report back.