http://www.youtube.com/watch?v=547BKysByqM&list=UUZ-qxagOkAmCEP-Tu6YliUQ&index=1
I was kind of surprised the .308 FMJ did not penetrate a 12" tree. Be interesting to see what the bullet path looks like inside the tree. I would imagine that M855, 5.56 AP and .308 AP would do much better.
I guess trees and log houses do provide reasonable cover. I remember my Dad saying that in the Pacific the .30-06 could often penetrate the palm tree trunks but no the Carbine round. Of course palm may be a very soft wood too, I don’t know.
Bullet stability is the key here. There are interesting photos in Hatchers’s Notebook on Pg. 406 and 407. One photo shows a 150 gr .30 caliber bullet penetrating 32 1/2 inches of solid Oak. The bullet was fired from 200yds and remained point on through the Oak.
The second photo is the same bullet fired into Oak from a range of 50 ft. Penetration is 11 1/4 inches. The bullet yawed in this case.
I would imagine that a 220 gr .30 caliber bullet would penetrate even more, being that round nose FMJ bullets are known to travel through materials like wood with minimal yaw.