I don't think it's "luck" that these were minor wounds, I think the brass fragments just don't have a lot of power to 'em and any resulting wound is gonna be pretty minor. 'Cept if you were VERY unlucky and got nailed in the eye because you were bent over or something but now we're talkin' real long odds.
The reason the bullets aren't going anywhere is that there's no "gas seal" behind 'em. Normally, a handgun powder charge would be set to burn across 4" - 6" or more of barrel travel, while the .308 needs 18+. Without that, 90% or more of the powder's energy is being completely unused, leaving 10% at worst to power the light brass frags.
Upshot: this isn't anything to fear losing life or limb over. It's more of a "bandaid and owwie" threat :). Mind you, I'm sure picking brass frags out of your hide HURTS, I don't intend to minimize that but y'all experienced the WORST that could happen, versus "luck".