It’s not like you’re carrying around chunks of elemental plutonium. They’re nuclear batteries. Read the description on the item.
They’re actually very uncommon - as firearms go in C:DDA - and the vast majority of Rivtech guns use one of two calibers of caseless ammunition. Their ammunition is about as unified as it gets.
They’re a new thing and they’re still a work in progress. But if we have triffids, why not evil electric-plants?
They’re really skinny zombies. Read the description.
Old stuff that predates the DDA project. They’ll likely get a makeover at some point.
Read more lab notes.
You’re wandering around after the downfall of civilization, the near-annihilation of the human race, and the end of the world as we know it. Of course there will be abandoned (by the living) FEMA relief camps scattered around. What part of their existence requires explanation?
Even though the questions were posed in a snarky manner, I’ve given you the best answers I have.
Remember that shortly before the cataclysm, there were increased military tensions with China. Heavy military presence and top-secret superscience were the name of the game in the days leading up to the end of the world.
As far as Rivtech goes, it’s a company that made !!fun!! stuff that helps to remind us that the world of Cataclysm: DDA is not quite the same as the one we live in. As it currently stands, it’s the same sort of vague behind-the-scenes existence that Twenty8, Doubletech, or any given one of the real-world firearms manufacturers that are mentioned in passing throughout the game has.