At lower velocities, 308 smaller game or varmint bullets (110-125 grains) penetrate deeper than what you would get from a 308, and so start to behave like a medium or big game bullet.
You can see this from the gel testing I had done after starting this thread:
http://www.300aacblackout.com/resour...t06OCT2010.pdf
For this reason, you have to toss your sense of what constitutes a normal bullet weight.