Thanks guys for all the helpful advice, it's all really appreciated.
Gary your a real gent mate & that's a really kind offer.
AR5s is at the shop at the moment for a test on there 'proper' Skan crono as it should be accurate, more so than a 'within 1% accurate' combro I really don't know.
Steve is a good technician on rifles & it could turn out there was nothing needed but a tweak.
ATB & thanks again everyone.