[jmr40]

SD only considers weight in relation to diameter. Everything else being equal higher SD's mean better penetration. All 180 gr 30 caliber bullets have the same SD regardless of bullet shape.

BC is a mathematical term describing how aerodynamic a bullet is. Long bullets in relation to diameter also tend to be more aerodynamic, but shape is also a factor. There can be a HUGE difference in the BC between a 180 gr round nose bullet and the very high BC 180 gr bullets.

With rifle bullets it matters. For example a 30-06 shooting one of the better 180 gr bullets will be moving at the same speed at only 75 yards as a 180 gr round nose bullet fired from a 300 WM. And the farther you go beyond 75 yards the bigger advantage 30-06 has. A 308 shooting a high BC bullet will pass 300 WM at 175 yards.

BC is rarely a factor with handguns. But SD can be.

As said earlier longer bullets in relation to diameter penetrate better. In the same caliber heavier is always longer and will always penetrate deeper. All other things such as bullet construction and impact speed being the same. But when you compare bullets of different calibers things get interesting.

For example a 147 gr 9mm bullet has a SD of .167. A 180 gr 40 caliber bullet has a SD of .161, and a 230 gr 45 bullet is .162. They are virtually the same with a slight advantage to 9mm. In real world situations penetration and performance will be about the same.

The 158 gr 357 load you looked at with a SD of .177 should penetrate a bit better than all of the above. But the difference between .177 and .167 isn't huge. Rifle bullets can range from .150 to well over .300. That makes a huge difference when shooting larger game. Most hunters want a SD of about .270 or greater for big game like elk, moose, etc.