One can 3d print springs. There are a number of thermoplastics that can be made elastic enough for such purposes. Though I imagine for simplicity, you'd probabl

One can 3d print springs. There are a number of thermoplastics that can be made elastic enough for such purposes. Though I imagine for simplicity, you'd probably want to go for a .25acp instead. Similar power, but using a centerfire round would be a lot easier to build a firing mechanism that would work given the limited number of shots you could fire.