Interesting problem. I have a short story that's serial apocalyptic, but there's no technology/weapon issue. Chase makes the good point that your readers are going to fill in the blanks. AE Lowen has mentioned the six-shooter, which if I were to extrapolate that to a future weapon I'm inclined...
I've spent entire weekends 'daydreaming' characters and their situations. Other days I'm just staring out the window with a wandering mind, which may or may not really be daydreaming.
I'm a pantster and plotting has not worked well for me. Since you have characters and you have settings, you might want to put one or more of your characters in direct conflict with the setting you've created. Build a scene from that. Let the characters try to get out or around the problem the...