Cartridge hybrid build log

[Skywalker]

Happy New Year! I finally got some time this winter break to put together a bolt-action gun to accept the cartridge I built last year(!!) Here's the scoop:




The bolt is a piece of 1/2" Sch40 PVC, with rings made of filed-down 1/2" coupler. The bolt slides inside a 1" Sch40 PVC pipe. The receiver is a piece of 3/4" PVC that I sleeved over the 3/4" EMT barrel shroud. (I had to heat it over a flame to do this, hence the dark color from the soot.) I put a spring in the receiver to help push the cartridge back against the bolt, but I'm not sure it's doing much right now.

JSR: I haven't done the work to turn the barrel shroud into the dead volume of a suppressor, but it's on my to-do list.

My next challenge is to make the electrical connections to the cartridge from my grill ignition (piezo) and mount that as a trigger. It'll also need a stock of some nature. I'll also have to tune the mixture ratios. This should be done by tomorrow (I have until Wedn to finish it!).

I also finally picked up a 300psi shock pump, and I made a jig to cut burst disks. (I'm using printer paper laminated with packing tape for the disks.) I tested the disk up to 300psi without failure.

[wyz2285]

Video? Looking good

[jackssmirkingrevenge]

yay progress! looking forward to seeing this roar

[Skywalker]

I added the piezo trigger on the handle, you can see it in the video. The video shows the ignition system, the bolt action operation, and firing / damage. It's done at 5x.



I had to reduce the burst disk thickness to one layer of paper & one layer of tape. If I had two layers of tape, it could hold a 5x without popping. The paper is necessary to keep the disk from wrinkling as I tighten the union, and the tape provides the sealing action. I also made a little punch for making the burst disks: steel pipe nipple and aluminum rod with a sharp edge.



I use the same trick that JSR used, flaring the base of a .22 pellet by pressing it against a .25 steel ball, to make the pellet fit the .25 barrel.



So, my project is almost complete! I doubt I will wind up making many cartridges (I only have one right now) b/c I don't have much time. But I did what I set out to do: made a cartridge hybrid from hardware-store supplies, using only hand tools (no drill press or machine tools).

[jackssmirkingrevenge]

very cool, kudos! Doesn't sound that loud on video either.

[Skywalker]

Edit: I want to move this to the showcase. Should I start another thread or can a mod copy the thread over?

It's a bit louder at 10x, but still nothing like a .22 rifle. Unfortunately the epoxy around the schrader valve cracked & there's a slight leak now in the cartridge. I'll have to rethink my design for next year I guess.
Here's a bit more in the way of damage pics:


It's a (fairly flimsy) steel case that housed a very old regulated DC power supply. I didn't realize until it was too late, but there was a vacuum tube inside it (!!)

I also shot at a more substantial case from an old computer, but the pellets wouldn't penetrate. A large finish nail did the trick tho! (The large holes in the plate are from my pneumatic gun.)

[Brian the brain]

Topic moved as requested..

[jackssmirkingrevenge]

If I remember well I couldn't penetrate PC hardware steel with my mini hybrid below 10x.

Above that though, no problem with lead pellets:



At 14x a lead pellets would go through two layers with ease:

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