This topic has been discussed and explained in great detail here ad nauseum.
In my opinion and experience, bullet SD is a lot like engine displacement. And as they say, "There's no replacement for displacement." Bullets with higher SD (i.e. heavier for caliber) tend to have higher BC, penetrate deeper, deflect less in the wind, and retain velocity at longer ranges than bullets of lower SD AND LIKE CONSTRUCTION. It may be true that we can get away with using bullets of slightly lower SD when using bullets of tougher construction, but SD is still SD, and that will not change. Tougher bullets penetrate deeper because they don't expand as much. If you shoot bullets that expand widely, then you need more SD (weight and momentum) to get penetration. Almost any bullet will penetrate enough to kill game shot in the ribcage while standing broadside. But if you plan to place the bullet on the shoulder, or if you plan to shoot at animals standing at a quartering-to angle, or any other situation that requires deeper penetration than the broadside ribcage shot, then you should consider bullets of higher SD. The SD of my current 7mm deer bullet is 0.31. I am slowly working into trying tougher bullets of lower SD, and so far have been successful on a number of occasions. The key is to use the right bullet for the application. In other words, "Use enough bullet."
Or you could use a TSX/TTSX & not worry about it.
