I really like the idea of carefully managing my very limited ammo, especially when I can control how each bullet behaves. I found the gun management aspect of the game to be pretty fun and compelling, but I think it would pair well with slower and more deliberate gameplay with more time to think about how I'm going to use my precious ammo.
At the moment, the shop interface is a bit unintuitive and kind of clunky (for example, it's really slow to change out bullets because I have to individually confirm each one I sell). However, I think I maybe understand what you're going for. Clicking and dragging things around gives it a really tactile feeling, as if I'm loading the gun with my own hands. With a bit more juice, I think it could be very fun to interact with.