Peregrine wrote:

This definitely goes against the fluff. Many novels have Marines taking hits from autocannons and continuing to fight. Though some of these appear to be based on the common Black Library error of referring to a heavy machine gun as an "autocannon," not all are. A Marine certainly can't take sustained fire from an autocannon, but could potentially survive a hit, especially a glancing one.

When I say wound, I mean a shot that goes through the armor. A shot that the armor stops won't be fatal (though it can still cause crippling injuries, by hitting an arm and snapping it backwards with enough force to break the bones, for example), but an autocannon shot that isn't stopped by armor is going to blow limbs off, or inflict instantly fatal injuries with a chest hit.

 Peregrine wrote:

This is right for Marines but wrong for Terminators. Terminator armor can withstand ridiculous amounts of force and still protect the guy inside-- in fact Terminators are substantially weaker in the tabletop game than they are in the fluff. In the fluff, Terminators can be stepped on by Titans and remain combat-effective. Similarly, there are fluff examples of Terminators being hit directly in the chest with krak missiles to no effect, and the old fluff about the origins of Terminator armor says it's tested by being dropped from orbit and that Terminators can walk around inside active plasma reactors unharmed.

It doesn't matter how well the armor survives, it's just a question of momentum. The energy of the impact has to go somewhere, and if a terminator takes a direct hit from a tank shell they're going to be flung backwards so hard that anyone inside the armor will be instantly killed. For a real-world comparison, just look at car design. We used to make cars out of heavy rigid frames for durability, which was good for preventing damage to the car from bumping someone in the parking lot, but in a high-speed crash all of the energy went into the passengers and you'd have a dead driver sitting in a mostly intact car. And then we realized that the best protection is to let the structure fail and absorb energy to protect the people inside. Armor is no different, at some point impact shock is fatal even if somehow the armor itself isn't damaged.

 Kingsley wrote:
I don't know what to tell you here-- multiple fluff sources have Terminators surviving ridiculous impacts (being stepped on by a Titan, direct krak missile hits, being flung by monsters, etc.) without any real damage. I think the explanation is probably "suspensors are magic."