I would also question the summary dismissal of SD as a factor in penetration. As in all comparisons, there are variables that affect the outcome. However, SD is simply a number that relates the relationship of weight vs. dia.
In a non expanding bullet, a higher SD will outpenetrate a lower SD given velocity and shape as constants.
In a non expanding bullet, higher velocity will outpentrate lower velocity given shape and SD as constants.
In a non expanding bullet, a pointed shape will out pentrate a blunt shape given, given SD and vel as constants.
In an expanding bullet, the list of variables must include bullet contruction. Among other scenarios, one can imagine two bullets of equal SD, shape, and starting velocity, but one with "soft" construction, the other "hard" Upon impact, the soft bullet expands to greater dia. therefore becoming a lower SD projectile. That softer bullet will pentrate less than the hard one.
We can also consider two bullets with identical SD, shape, and contruction, but different impact velocities. In this case, the higher vel. will generate greater expansion and therefore lower post impact SD. The greater expansion, (lower post impact SD) may actually factor out the penetration advantage of the higher impact velocity, and cause the slower bullet to penetrate farther than the faster one. This explains why say a 6.5 x 54 MS might out penetrate a 264 WM when all other factors were the same.
Obviously, the variables are so significant, that definitive statements are difficult. I would however, state that when all other factors are totally equal, higher SD offers a great indicator of penetration potential.
JimF
