What sort of parameters are you looking at?

If you want simple & cheap - & especially disposable - then it seems to me you’re talking about a one-shot weapon that would be built around the cartridge. Point, shoot, throw away. I don’t see how anything could be cheaper & easier than that.

If you’re talking about reloading at all, that complicates the mechanism. If you’re talking about making it any kind of repeater, even a revolver, that complicates the mechanism enormously.

Any kind of multi-shot capability also makes it harder to make the weapon safe to fire. Whereas if your cartridge is simply sealed permanently inside the weapon, it becomes a lot simpler to contain those nasty, hot, high-pressure gases, and make sure they only come out the one hole in the front they’re supposed to.

There’s also a question of how you envision these things being fabricated. What advantage do you see in using polymers? Metal, metal-working tools, and metal-working skills are widely available. You can right now name a metal - steel - which is safe for making firearms and also readily available, even abundant. It even comes conveniently made in a wide variety of shapes which might be used or readily adapted for use in your design.

BTW, I got the first issue of American Gun Culture Report, and it’s awesome. I highly recommend it - hell, consider