You're missing the point. The reason four layers of denim is used for ammo testing is to see whether or not the bullet will expand repeatedly after encountering these materials. Ammunition designed to meet the specifications as outlined by the FBI Ballistic Test Protocol is engineered to expand after encountering obstacles like plywood, automotive glass and sheet metal.
This is mentioned in my previous post on page 2
http://greent.com/40Page/general/fbitest.htm
I find it curious that people spend lots of money on what they personally consider to be their perfect defensive handgun, yet still use ammo with questionable attributes. Just because Hydra-Shok ammo is old doesn't mean it's good. W-W Silvertips have been around since 1979, does that make them the best choice? If there are better choices available that will expand after encountering a wider variety of obstacles wouldn't you rather use that?
Bullet R&D has evolved in the thirty years since those dated designs became available.
Nothing is a sure thing. Prepare for the worst-case scenario, not ideal conditions. Have a back-up plan in order. Do you think the bad guy is going to stand still and let you take careful aim between his eyes? You may only get one shot off; make it count. This isn't a fairytale or after-school special that always has a happy ending.
There are no magic bullets, but modern bullet designs will increase the odds in your favor.