Their system gives a tighter bushing fit to the cylindrical barrel so the relationship between the foresight an the barrel is more consistent, the screw is removed because if it's left in the differences between barrel and slide alignments cause friction, wear and cycling problems,Blackstuff wrote:http://www.aw-armoury.co.uk/gsg-1911-74-c.asp
Its bizarre because once the kit has been fitted and screw removed, the barrel has much more 'slop' in it, in relation to the frame, but somehow accuracy improves?! I'm not going to argue with the results though :)
Regards,
Nick