## 2 thoughts on “Trope-a-Day: There Is No Kill Like Overkill”

1. Speaking of overkill a rather boring weekend lead to me running some stats from your IL-15i Battlesystem. If I was anywhere close in my math that standard rifle will have a meat penetration of over 14,000 U.S. miles. I took the mass and size of a grain of sand slug of iron and the (best estimation from you mentioning at one point “significant fraction of the speed of light”) mind-crogling speed of 40% light speed of said slug.

14,000 Miles of penetration from a single handgun means that it could probably kill the guy and the building he is in.

Even if I was hilariously off that is one scary common weapon.

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• Buggy

Bit late here, but you are off a fair bit, yeah.

The main problem is that you’re using a simplified calculation intended only for your typical metal bullets travelling within a order of magnitude of the speed of sound. It assumes things like, for instance, the bullet will remain largely intact if it hits something much softer than it, or that it’s physically possible for the intervening matter to be pushed out of the way.

At high speeds, that doesn’t happen, because the forces involved scale exponentially with speed. Anything in front of it would have to be given more acceleration to be pushed out of the way, and the projectile itself is under much more stress despite it’s smaller size. This starts to violate normal ‘slow bullet’ physics at even human-achievable rail gun speeds (aka single or low double-digit mach numbers).

At 40% of the speed of light, chemical bonds are basically irrelevant. You have a collection of loose atoms, it’s largely irrelevant whether they’re solid or a dense cloud of ions, stripped of their electrons by the fields that accelerated them. Same with whatever it hits. The physics are closer to “unusually dense packet of moderately-high energy heavy-ion radiation” than a solid projectile, and you could probably get a okayish figure for penetration by following that route. With the caveat that normally those figures don’t really account for the radiation being so dense, that you have to worry about the momentum it imparts to whatever it hits.

I’m not entirely sure how to calculate that, actually, but as a ballpark estimate, alpha radiation has about a tenth of the mass, a fifth of the mass… and is easily stopped by a sheet of paper. So probably something like “1-2 sophs’ worth of meat penetration, but whoever you hit, you really ruin their day”.

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