MAC tries out 4 defensive ammunitions using ballistic gels and how it performs against some barriers.
This test should be taken with some grain of salt. There are studies done under better and more controlled manner. Furthermore, those studies indicate that permanent cavity is more important than temporary cavity(or stretched). Whie it is impressive to see temporary cavities, the importance goes to permanent cavity
The bulletproof vest test at the end did not mention that +P+ rounds are closer to .357 magnum rounds which is beyond what Level IIA armor is rated for. So there is no surprise that the +P+ would penetrate.
From: Military Arms Channel