I got to work on a compact 45 cal sub-machine gun a few years ago. We did some conceptual work for different models and redesigned the folding butt stock.
This specific weapon improved muzzle climb and re-directed the recoil forces so the embodiment was different than your typical AK47, M16, etc. From the innovation aspect it was awesome to work on it. Solving ergonomic and usability challenges was also challenging.
It’s hard to draw the line as to what you will and will not design. We live in a society where our police and military use weapons. Our TV shows, cartoons, video games and movies glorify weapons and killing. In my opinion the amount of violence our society watches as entertainment probably causes more harm than the actual gun.