After fitting the trigger kit, i finally got round to having a play with my new 17Mach2 CZ American on New years day. Seemed to be shooting ok at first but then groups started to open up(possibly fouling in the barrel, also need to float the barrel fully). On returning home i emptied the spent cases from my coat pocket to find a number of them had split on firing, looking on RFC showed this was a problem with some Hornady ammo(which i was using) and on checking the remaining 3 and a half boxes found nearly fifty cases with split necks.
I am hoping this was the reason for the iffy grouping and at least now i can elliminate this factor.