We've all endured the various debates about handgun cartridge effectiveness. We're told the venerable .45 ACP is capable of physically unfeasible things, while the 9mm will annoy an assailant at best. While some folks have conjecture and anecdotes, I have physics on my side.
It's all about black holes, specifically the Schwarzschild radius. That's a measurement of how tightly a given object must be compressed in order for it to become a gravitational singularity. For example, the Sun would have to be compressed to a radius of roughly 3 kilometers before it became impossible for light to escape its gravity.
The Schwarzschild radius for the Earth? 9mm. Yeah, science!
You don't get better stopping power than something that rips a hole in the fabric of spacetime.