Thanks Robin that just about puts it to bed then, the reason I was really asking is the Match sight that came with my rifle was missing the mark by 5-6mm to the right on a rest every shot and wouldn't adjust any more, this morning I completely removed the sights and centra rises and rebuilt the lot, I found the risers has the spacer tubes in upside down so, although you couldn't really feel it, there was play between the sight and rifle, I now have done a quick test (one shot @10m) and even without any zeroing it is very nearly bang on, so no I wont be bothering with a new sight now