Interesting video of the guys from Valor Ridge testing the penetration of some popular standard and HD 5.56, 7.62, 9mm, and even some .308.
http://www.youtube.com/watch?v=PbdmQ5IN2j0
Some of the rounds tested include standard Ball, Speer GDs (two different weights), TBBC, SMK, & HST. Nothing earth shattering but some of the results were a bit surprising. My favorite takeaway...
..."Refrigerators aren't cover."