Alright I leveled up the old save and took Living Anatomy and did some intensive testing here are the testing results.
First test was against against ED-E who has a DT of 8. and as a companion I could easily view his HP
*with companion nerve DT of 12*
I did this before taking the perk as Living Anatomy increases the pipboy display of damage but doesn't actually robots.
Sniper Rifle 42dmg:
Regular .308:31DMG. (42-12DT=30)
AP Round 41DMG. (42 x0.95=40)
JSP Round 46DMG (42-12DTx1.5=45)
All of these mathematically were off by only a single point of damage. However a stray decimial point normally hidden from us caused by lord of death can easily account for that.
After getting living anatomy the real testing began first on some nearby fiends.
Base DMG 45
Fiend=DT 5. 70HP
Regular .308:40DMG. (45-5DT=40)
AP Round 42DMG. (45x0.95=42.75)
JSP Round 60DMG (45-5DTx1.5=60)
But how does it fair against those guys in black armor? My test subject had 270HP and a DT of 24.
Regular .308:9 DMG. (45-24DT=21)
AP Round 21DMG. (45-9DTx0.95=34)
JSP Round 9DMG (45-24DTx1.5=31.5)
It didn't appear to matter if my sniper rifle was silenced, unmodded or the gobi.
I then tried other weapons, like the dinner bell loaded with slug rounds. Its listed damage was 80. And as a slug DT would be applied once.
Dinner Bell 80dmg base[*remember slugs are a single projectile*)
Slug: 31dmg (80-24=56) The damage is off by 24.
Mysterious Magnum: 45dmg base
.44: 9dmg
From here we can tell the problem isn't the sniper rifle, I tried a couple other weapons and the damage was still off.
So then I moved on to a nearby unarmored ranger.
She had 195HP 0DT
Sniper rifle dealt 35dmg.
Mysterious Magnum: 35dmg
Dinnerbell: 56dmg
My conclusion is that rangers have a built in damage resistance, one that is probably applied before DT.
My response to Granite and the thefalloutfanboy
Spoiler
Mathematically speaking a 50% increase in in dmg should counter the armor almost as well.
45-24DTx1.5=31.5
45-(24DT-15AP)x0.95=34.2
IE 45-9DTx0.95
Your completely missing his point to, he's saying the damage vs a ranger is FAR lower then it should be and he's RIGHT, I just proved that using Living Anatomy.