Walt I've been trying to figure out good stats for railguns and shield penetration, but I've been having a lot of trouble. Ideally IMO railguns would deal almost the same damage as right now vs internals, vs armor, vs 1 shield if ~8 extenders, or vs 2 shields if ~26 extenders (which are the two "critical points" that people use right now - different lengths aren't very useful most of the time).
Here's the spreadsheet I've been using if you want to take a look: http://www.mediafire.com/file/pnpf3v1ce1s7i3n/zzzstats.xlsx
Outputs are far to the right. Ideally all the light orange cells in the output columns would be around 100%, meaning that the new railgun would deal around the same total damage as the old railgun. The green cells represent those two critical points that people build at. The light yellow cells are expected to be massively higher than 100%, since right now railguns are effectively worthless at those sizes/vs those shield counts. "Baseline" represents how much damage railguns currently deal (note the huge jumps at 8 accelerators vs 1 shield and 26 accelerators vs 2 shields).
I might have glaring math error somewhere in there though. The spreadsheet does remove wasted overkill damage. The "Automatic" cell in column H calculates the minimum shield penetration resistance that can prevent railguns from penetrating without destroying the shield first.
Walt It means that, like it currently works, the railgun will pierce the shield if it does enough damage to bring it down, but will lose penetration and thus damage when it does.
So a theoretical weapon with extremely high penetration and low damage would still not be able to pierce a shield? IMO shields should behave just like other parts, so if you have enough penetration you can cut through the shield, even if you have low damage (like an electrobolt). Plus this would allow for potential new shield-like parts that reduce damage, but don't completely block it.
Though IMO the railgun should be balanced so that if it ever has enough penetration to penetrate a shield, it also has enough damage to break the shield when it penetrates. I think that ideally the railgun's damage to penetration ratio would be exactly the same as a shield's damage to penetration ratio. That would both prevent the railgun from penetrating without destroying the shield without needing a special rule, and would prevent awkward cases where you destroy the shield with plenty of extra damage, but the projectile runs out of penetration and disappears.
I also think that physical parts, not just shields, should lose penetration resistance as they get weaker. Aside from also helping to reduce reliance on critical points, this would also help cannons and railguns synergize better and IMO is more realistic (the parts literally have holes in them). I personally think that both shields and parts should drop from 100% -> 50% penetration resistance as they drop from 100% -> 0% health. This is allll just my opinion though.
Also, my previous suggested stats for the small cannon were badly off. I calculated that based on per-room penetration damage instead of per-tile.