Joined: 15 Mar 2007 Posts: 18061 32519.23 Spud Bux
My attempts at prototyping this design didn't go too well, but combining the valveless idea with cartridges was too appealing an idea to give up so gave it a bit of thought recently on how to improve it and came up with pretty much what I had proposed initially. I decided to give it a go for 0.177" calibre with a 6mm tube cartridge, and results so far are very encouraging.
Here are a couple of videos at 420 frames per second, with the cartridge unsupported it will happily put a BB through an empty soda can, in the next shot the cartridge is resting against a weight and this way it punches through the bottom of a soup tin.
Here's the cartridge popping out of the breech at 1000 frames per second, comes out with quite a bit of force so it should have no trouble ejecting itself and pushing a bolt back far enough to reload a new cartridge.
Seems like the work of making a ton of those bb cartridges may be better spent on your previous "stepped piston" dakkadakka design with a .177 barrel.
A high-capacity mag could simply run parallel to the barrel(a staplegun spring or two might work well here).
Of course, if you're just looking to spew brass on the floor, then by all means carry on.
Joined: 15 Mar 2007 Posts: 18061 32519.23 Spud Bux
Fnord wrote:
Of course, if you're just looking to spew brass on the floor, then by all means carry on.
Of course the fact that you're using the air to cycle the mechanism means it's not as efficient as it could be, but I think we've established the importance of the "brass spewing" feature to yours truly by now
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If this works...are you gonna finally make a complete gun for it?
That's the idea, I'm going to graft a spring loaded bolt to this breech and see if it can handle cycling the action and move on from there.
This is vaguely what the test rig will look like (along the lines of my earlier prototype), I've gone for a tension spring for the sake of keeping things compact.
I added another spring and positioned a cardboard box for the bolt to strike but to no avail, it was still thrown out of its housing, then whipped away by the springs
As to power, all the above shots went through one side of a zippo lighter fluid can and almost made it all the way through - not spectacular but good enough, certainly better than my first cartridge fed pneumatic effort that couldn't make it through a sheet of cardboard one should consider that the "chamber size" is basically the cartridge, so while it is at high pressure there is a relatively tiny quantity of air pusing the projectile, perhaps a wider/longer cartridge is in order.
All in all, it certainly looks like it has enough power to work a magazine fed cartridge setup, as a proof of concept this thing is working remarkably well
Instead of that mess of wires and springs, why not house the bolt in a half-pipe of sorts, with a compression spring, instead of an extension spring (which introduces the possibility of breaking both the springs and wire restraint all in one go)?
Joined: 15 Mar 2007 Posts: 18061 32519.23 Spud Bux
saefroch wrote:
Instead of that mess of wires and springs, why not house the bolt in a half-pipe of sorts, with a compression spring, instead of an extension spring (which introduces the possibility of breaking both the springs and wire restraint all in one go)?
This is just a proof of concept prototype, for an actual finished launcher I'll go for something neater. This is only to see if the idea can be made to work.
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Once you're pretty satisfied with a cartridge design, you could order a bunch of them (or at least everything but the seal) from a machine shop.
The cartridges are really the simplest thing to make, it's just a section of tube, sealed with araldite at one end and with a section of silicon tube epoxied in on the other, and four ports drilled through it.
As the seal releases the BB well below the 800 psi I'm feeding into this thing, I thought I've give it a go with a ball valve closer to the breech to see if it gives better power but judging by the zippo can penetration it doesn't make much of a difference.
nice
You might encounter more problems when you add a mag. That might be a bit tricky but I am sure you can get it to work right.
Ohh donw't forget that you can delay the bolt with the use of a simple check valve
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why not house the bolt in a half-pipe of sorts
ohh you see ? other people have suggested the same thing
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one should consider that the "chamber size" is basically the cartridge, so while it is at high pressure there is a relatively tiny quantity of air pusing the projectile, perhaps a wider/longer cartridge is in order.
