Alpine-
The S.D. "rule" applies more aptly when you are shooting bullets of similar construction. Here, a 180-gr Nos Part which loses 40% of its mass probably won't out penetrate a 168-gr TSX because it loses little if any significant weight. This is assuming of course similar speeds and hits.
Back when I did my wet, packed newspaper penetration tests with my .340, the 225-gr Nos Part was out-penetrated by the first generation Barnes X of 210 grains and significantly more by the 225-gr Barnes X.
This is not an indictment of the Nos Part but just points out their different construction and how S.D. does not automatically corrolate with greater penetration.
