Scoring hits is where you get attack value vs. defense value - the actual mechanic is picking a random number between 0 and each modified value, and then comparing them. The part that's poorly explained is what happens next, and the manual doesn't really go into details: something determines if it's a Retreat Hit, Kill Hit, or Pinned Hit. And that's the part where auto-kill overrides normal mechanics.
[All that doesn't apply to shields; they automatically force misses but lose HP every time until they're depleted, at which point they're immediately killed. They also don't replenish from one combat to the next, or receive defensive modifiers from commanders, etc. This is why personal shields are such garbage, though they're better than they used to be. IIRC, they now lose fewer HP from hits that don't exceed their defensive value - might even be none. Basically, what's good about them is that it's hard - I want to say impossible? - to get an immediate kill on them, but given time they
will die. Again, the mechanics are funky, and I had to do multiple attacks and pick through the details combat report very closely to
figure out what was going on. How Vic precisely changed that is lost to the mists of time since the changelog doesn't go back that far, but again, I vaguely recall it being that doing less than the shield value reduces/eliminates the shield loss.]
I searched in vain to find a list in the manual with the kill percentages were for atomics, and I finally realized that Pymous had listed old vs. new in
a design document for their retuning mod. The manual never actually mentions them, unlike SAM kill stats. The numbers are 30% for 1MT, 50% for 10MT, 70% for 50MT, 90% for 100MT. Micronuke and atomic cannons are also both 50%. SAMs are 50/60/80 depending on size.