At the price of premium ammo, running 2 full magazines or more gets expensive fast...
Elvishead,
The shape of 9mm FMJ seems to be a good penetrator all by itself. But if you've gone through 8 rounds not making a hit or not an effective hit, the presumption is that you're behind cover, getting behind cover, finding concealment or impersonating Jessie Owens doing the 100-yard dash!
That about somes it up. I empty my mags by shooting them so I'm only losing 7-8 SD rounds.