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Re: preloaded pneumatic cartridge

Unread postPosted: Wed Nov 15, 2017 9:55 pm
Author: hectmarr
A question. What is the advantage over a pre-compressed air gun with a camera, a PCP, of this system of cartridges?
The smaller size of the weapon when there is no air tank? Is the pressure you use greater?

Re: preloaded pneumatic cartridge

Unread postPosted: Thu Nov 16, 2017 6:32 am
Author: jackssmirkingrevenge
One of the greatest personal incentives to me is having a mechanism that replicates that of a firearm, long time members will tell you of my fascination with shell ejection :) Some other practical advantages include the possibility of a repeater with irregular projectiles (such as a shotgun), having the leak-prone pressurized mechanism restricted to an easily replaceable cartridge as well as the opportunity to create a variety of different cartridges that can all be fired from the same launcher.

In the meantime I've crunched some numbers and figured some practical mechanics, here's what a high pressure exhaust valve cartridge wold look like for a 3/8" ball bearing, 0.75" diameter and 3" long making it roughly the size of a shotgun shell.

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The front end is permanently pinned in place while the rear is removable for maintenance purposes. The piston is machined from a single piece of delrin, and I envisage filling being done through the mouth of the cartridge via an appropriate fill rig. Not shown is a groove or rim for extraction purposes, I'm still debating if this will be necessary - technically it would be easier to extract a shell that for whatever reason didn't fire, but the same can be accomplished by pulling the bolt back and letting it fall out by gravity - not exactly elegant engineering, hmmm...

Re: preloaded pneumatic cartridge

Unread postPosted: Thu Nov 16, 2017 6:57 am
Author: hectmarr
A question. When it is fired, the oring comes out of its housing, where is the spring, escaping the air of the pilot there?

Re: preloaded pneumatic cartridge

Unread postPosted: Thu Nov 16, 2017 7:12 am
Author: jackssmirkingrevenge
This is how I envisage the firing stem, with a flat machined in it to allow air to flow past the o-ring:

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Re: preloaded pneumatic cartridge

Unread postPosted: Thu Nov 16, 2017 8:01 am
Author: hectmarr
Is that so? If you do not correct me ...

Re: preloaded pneumatic cartridge

Unread postPosted: Thu Nov 16, 2017 8:17 am
Author: jackssmirkingrevenge
More like this, the stem is not airtight at its widest diameter so it should leak with minimal movement:

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I also envisage the spring being very weak so as not to encourage the stem to re-close as the piston recoils.

Re: preloaded pneumatic cartridge

Unread postPosted: Thu Nov 16, 2017 9:14 am
Author: hectmarr
Ok now I understand well. Good design in my humble opinion of neophyte. Thanks for the clarification.

Re: preloaded pneumatic cartridge

Unread postPosted: Wed Nov 29, 2017 7:40 am
Author: jackssmirkingrevenge
More practical musings, perhaps a mechanical lock is a better idea.

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Re: preloaded pneumatic cartridge

Unread postPosted: Wed Nov 29, 2017 10:06 am
Author: hectmarr
It seems a little more complicated, without this being a problem.
Question: What material is indicated by the red arrow?
What are the advantages compared to the previous design?


Note:
There is NOTHING to replace your practice of having seen thousands of these mechanisms .... :|

Re: preloaded pneumatic cartridge

Unread postPosted: Wed Nov 29, 2017 11:02 am
Author: jackssmirkingrevenge
Question: What material is indicated by the red arrow?


Those are steel balls, the function is like an airsoft grenade:

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They hold the piston in place in the same way that a quick-connect fitting works:

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What are the advantages compared to the previous design?


No air is wasted for piloting, and piston release is instant, there is no pilot chamber emptying that will slow the piston down. It's a little more complex to make, but also more reliable and in theory faster opening. If the difference in diameter between from and rear o-rings on the piston is small, the force needed to actuate it will also be minimal.

Re: preloaded pneumatic cartridge

Unread postPosted: Wed Nov 29, 2017 3:31 pm
Author: hectmarr
The fact that it opens faster is important. I like it. :bounce:

Re: preloaded pneumatic cartridge

Unread postPosted: Fri Dec 15, 2017 8:35 pm
Author: hectmarr
Hi Jack :) How is the construction of the preloaded air cartridge? Could you advance something on this topic?

Re: preloaded pneumatic cartridge

Unread postPosted: Sat Dec 16, 2017 5:20 am
Author: jackssmirkingrevenge
I've been distracted by other projects :)

I current have a box of parts that used to be one of these that I would like to turn into something like this:

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Re: preloaded pneumatic cartridge

Unread postPosted: Sat Dec 16, 2017 6:15 am
Author: hectmarr
It looks interesting. The line of this weapon is very pleasing to the eye.
On the other hand, I've been doing nothing until. These days I will resume the tests.

Re: preloaded pneumatic cartridge

Unread postPosted: Wed Jan 03, 2018 6:21 am
Author: jackssmirkingrevenge
In conjunction with a nice rifled big bore barrel and a Crosman 2240 grip, I think something like this is looking feasible:

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Single shot and perhaps with enough force to blow the cartridge back and eject it.

With a good bit of force behind the bolt I think I could go with a spool design:

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GGDT suggests performance within my expectations at 3000 psi:

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Even with the pressure balanced, there will still be a substantial amount of friction on the o-rings, I wonder if it would be worth unbalancing the spool slightly with a bias towards opening.