DaDave's spring was too strong, so I poked some holes in it using fusion 360.

My rudimentary tests show that it has vastly decreased the tension, allowing you to shove more darts in the magazine, and not worry so much about them being squished.

My guess is that it will wear down pretty quickly, so this is still a WIP as I print more magazines to try it with.

You don't have to use supports if your printer is good at bridging.