Just jumpinback a little bit here... but I've never heard of any high-caliber rifle bullet have velocities so fast that they "zip right through a deer." I'm not sure on the ballistics of the .308 and 7mm mag... I'm a .270 person. I've heard that the .308 and .270 are similar in ballistics.

And plus, bullets will expand/penetrate differently with different types of bullet and "matter." Example: a .270 winchester ballistic tip will penetrate/expand differently in dirt than on an actual deer.