"shooting a mass of uranium down a barrel into another mass of uranium to form a supercritical mass."
My guess is that the person who first said that didn't intend for the metaphor/description to be taken quite as literally as everyone ended up taking it. (Or they meant to mislead.)
Hypothetically, if you read "into" as crash/collision and not "in to"/inside of, you start to see how a generic description could be ambiguous. Run this (or a similar story) through a few iterations of the telephone game and draft revisions by journalists/editors (that somehow all seem to graduate without ever taking a single sophomore level technical writing course), and a description becomes a misunderstood metaphor becomes a fact. Somewhere along the way, the word "bullet" gets thrown in, and then no one "un-see" the visual.
That's my take. That and the author of tfa is trying way too hard to make a big a deal out of it being a "gendered" thing, when it's not.