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I have put this on hold because I will not be able to do a build until summer and the feedback seemed to be counter what my initial design goals were. I am going to continue to iterate until I get to the point for a build, so going to try to respond to all of this great feedback now. Made all my responses in order of post.
The goal is not an easier to build blaster. It is for something that is more durable and with ease of serviceability. I am not that concerned with the difficulty of slots, they are good for the attributes I want. These are also easy to create a jig for, which I will be doing. no considerations for mass production, this will be a DIY project and CC BY-NC-SA 4.0.
It is not designed for PVC, it is polycarbonate 1.75-1.5" tubing. Better stiffness and way higher impact resistance. Would not be compatible with any PVC sizes for the upper receiver.
For the half dart vs. full dart argument, if I had to design for full darts I would just say go with an existing design. If there is no value in a half length only blaster I don’t see much point in going forward with this. Using the half length gives me several design wins. Shortens the maximum arm extension; better ergonomics and arm angle for priming. The bars on the charging pump can be exactly 12 in, good for part sourcing. Cuts a big chunk out of deadspace. Reduces the mass, overall length and print volume.
I will say I may have been mistaken at the prevalence of katana mags by seeing the nerf community mainly through the sort of people who are always onto the latest thing.
Are pump grip 3d print failures on the caliburn an issue? Would be easy to design something to use a tube for the outer part of the grip, but without serious milling the inner portion will still be 3d printed.
Breach designs are very interchangeable. Pusher or sleeper style brass could be done with the same bolt. Others might require a different trunnion.
Some notes on disassembly. The butt-plate should always be removed first during servicing so that the spring is not under tension. The only operation you can do without this is a barrel swap. That could be done without removing the front cap, but it may make it easier if it is removed. The barrels are friction fitted into the trunnion. To remove the plunger, only the butt-plate needs to be removed. To get the bolt out is more involved. First the butt-plate, then lower receiver, next the trunnion and front cap.
The rail section will be permanently glued to the upper receiver as seen in the exploded view. Should be no issues with durability.
The draw and preload are exactly the same as the caliburn, if those are not desirable I can adjust. Would not be able to have variable draw lengths once built due to seer design. Already planning on testing some really long barrels.
The lower receiver might be able to be 3d printed, but it has one very important high impact job, the two upward facing teeth are what catch the bolt when the plunger impacts it. Not sure if PLA is up to the task there.
As to lathed bolts, I have drawings done for HK style push pins. Could mill or 3d print the bodies and make springs from wire.
I explored using the barrel as the charging arm, but then you need a push forward stoke to load instead of just pumping. Also makes barrel swaps a bit of a pain. There are some interesting designs I can think of using that method, just not for this blaster.
The bolt does not transfer the plunger shock to the ramrod, it goes into the lower receiver. Again see the teeth on the top of the lower receiver in the exploded view.
The o-ring in the trunnion is easy to leave out if it causes feed issues, it is not necessary to the sealing with a brass breach.
*had tube ID wrong
