Basically in most cases armor is not expected to stop most threats (though it obviously works against lower threats), but instead it is meant to keep you alive if you are hit by lowering the damage.

Basically with the power available in ETC weapons carrying enough armor to stop an enchanted penetrator/hyperdense bullet is not practical, so what you are trying to do is to:

• Force the enemy to use AP ammo so you get lower damage multiple after armor.
• Reduce the base damage enough to make low number of hits survivable.

Being hit by the standard imperial infantry rifle using the combat round “Standard combat”: APEP 3d+2(9) pi or increasingly the HD round coming to service: “new combat”: APHD 3d+2(15) pi.

Against likely armors and a soldier type with maybe 12-15 HP:

• Non military: Nanoweave Tacsuit DR 30 or the new:Monocrys Tacsuit DR 40 the armor has really no effect reducing 2-3 points still leaving 3d-1 or 3d, but both are survivable as single hits with a normal of about 10 points (major wound and likely reeling) to a maximum of 18 points(below 0 points but fairly far from death)
• Against military medium armor a Commando Battlesuit at DR 105 the weapons still penetrate as the armor stops 7 or 11 points, resulting in 3d-5 or 3d-9 points, here the armor reduces the damage considerably for an average of 1 or 6 points though(making it possible to continue fighting after a few hits) and a maximum of 13 points though, that might not even be below 0 hitpoints.
• Of course if you are in really heavy armor: Heavy Battlesuit with DR 150 over the strong areas the suit reduces the damage by 10 or 16 points allowing about ignoring the old style combat ammo(90.74% of no damage), and likely taking very little damage from the even the HD ammo, on average roll you take 2-3 damage and on the worst possible case you take 10 points, that is not enough to take you below 0.

Of course if you are in a Heavy Battlesuit you are more likely to be targeted by something heavy military like your own rifle, the 15mm etc rifle

The same really goes for pistols and civilian type armor too, without armor the enemy can fire a 10mm heavy pistol loaded with hollow points for 3d pi++ pistol shots at you causing average of 21 points through that might easily be a death roll on a civilian…

But even with a nanoweave vest that is 0.9kg/DR 18 and is easily concealable under clothes they have no hope of penetrating even with standard ammunition, not to mention the hollow point. With basic AP ammunition 3d(2) pi they likely penetrate for an average of 1.5 points of damage.

With the enhanced penetrator they do 3d(3) pi and on average do 4.5 points, that, while a few shots might be fatal, you are far from the single shot death possibility from the hollow point and no armor.