This is amazing, CaptainSlug. Well done. I've been wanting to build a mag-fed, pump-action blaster for a while. Thanks for the great write up. I might try to implement this.
I have a question about the plunger rod. I notice you're goal is to reduce inner cuts with the scroll saw. Effectively reducing the difficulty in making the blaster. Inner cuts can definitely be pretty annoying to accomplish. But the rod plunger rod is also tricky because you need access to a machine lathe. I like to use square plunger rods because they're easier to make. They can be cut with a scroll saw and they don't rotate so they only need a notch on one side. I wonder if you've ever considered a reuleaux triangle drill bit. They allow you to drill square holes. Since the plunger rod is only one size, you'd only need one special reuleaux bit for the whole project. This might enable you to use a square rod and eliminate the machine lathe process.
I ask this mostly because I am considering doing just just if I duplicate your design. Not necessarily to try to sway you toward square rods yourself. I'm wondering if you have thought of this and think there's some reason to go with the round rod anyway or was it just not considered?
The reuleaux bit is a really nice solution that I think should be more well known in the NerfHaven community. There's a lot of square holes out there being cut with scroll saws. In general, most plunger rods are the same size too, so most nerfers would only need one bit total in their shop. I actually use an X-Carve CNC for my templated cuts so square is really not a big deal for me anyway.
Well thanks for the great write up! Looking forward to seeing any tweaks you make to it.