I was thinking of something else we have left out of the equation, ballistic coefficient. The "BC" of a full WC may make it difficult to get it to shoot accurately at 100 yards, which for some reason seems to be the object of the OP. Another thing is that shooting them with light loads, as they were designed to be shot, my not get them stabilized enough to be accurate at that distance either.
Not only is it too small of a sample but too many variables to be processed definitively. There are other lead bullets with better BC, I wonder if he has tried those. LRN, LTC are a couple that come to mind. The 173gr Elmer Keith bullet might be a good performer at that distance too, if driven to the correct velocity.
Here is a post from lbtmoulds.com. It might be worth reading before such a generalized statement is made. The title of the thread assumes that no one has achieved better accuracy with lead. In order to state that accurately, one would have to know that NO ONE has ever had it the opposite way. I would disagree.
JACKETED PERFORMANCE WITH CAST BULLETS
By Veral Smith
This illustrated booklet is recommended reading for all bullet casters, especially beginners, but even for those with 40 years experience. It has information about cast bullets which you won’t find anywhere else, and covers every important factor about making and shooting lead bullets. It explains how to do it, the scientific answer to things that can go wrong, why, and how to correct any problem. Has Veral's new formula on killing power which dispels the other theories and myths (unscientific and unprovable notions) relative to killing power, and explains what actually makes a bullet kill. You’ll know and can prove the whole book is fact, and learn that the author despises theory, on anything!
It's like an atheist saying that he KNOWS there is no God. Someone needs to ask him if he knows everything. If he is honest, he would have to say no. Then the question needs to be asked; "Is it possible that in that section of knowledge you don't have, that there is a proof, solid and verifiable, and beyond a shadow of a doubt, that there is a God?" Again, if he is honest, he would have to say, yes, it is possible seeing I don't know everything. They could say that they haven't seen the proof and be quite correct, but to say that there was none is totally incorrect.
Same as this: "Jacketed bullets are
ALWAYS more accurate than lead." In order to say that and be correct, one would have to know that
NO ONE has ever had it the other way.
FWIW