As best I can make out from your comment, if you are using a replica "T" or bracket or both, it could be your set up is not properly done so that there is insufficient travel in the lead screw to both zero the scope and have full adjustment up to 1000 yards. What do you mean by the lead screw having been shortened? It is shorter than the windage lead screw of course, but there should be no need to shorten it from the original.