Good. Tell me what he thinks; I don't actually know the answer.
I was just thinking about the implications of a railgun slug containing a chunk of weapons-grade plutonium just under critical mass... when it hits something at sufficient speed, the pressure of the impact should compress the plutonium enough that it goes nuclear. Bye-bye, Nagasaki...
NOTE: This was not meant as any kind of insult to Japan or anyone living there, or any indication that I think Nagasaki or any city should be nuked again (which I don't). I referenced Nagasaki because it was the first thing that came to mind, and because the "Fat Man" nuke dropped there was based on plutonium and relied upon physics similar to those in a supersonic collision as described above, as opposed to the "Little Boy" bomb dropped on Hiroshima, which used two separate chunks of uranium. Theoretical nukes? Fine by me. Actual nukes? *insert NO! GOD NO! gif here*