Often as I'm trying to cram all my equipment in a backpack I start thinking: 'if only there was a speedloader as big as my arm that could save me a second or 2 in loading time'.
I could build something better with a funnel, parts from a high cap mag, a broken hop unit and a cranking handle. It would be easier to use and smaller. But would it be worth the hassle?
Take a high cap, remove the spring, connect a handle directly to the wheel that pushes the bb's and glue the lower part of a hop unit into the hole at the top so that you can then press your low cap onto the device and turn the handle to load the mag
If you think you could do it I'd say go for it. I don't know if you get a lot of spare time but you seem fairly confident and probably pretty good at making stuff so I think it'd be great to try.