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preloaded pneumatic cartridge

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Re: preloaded pneumatic cartridge

Unread postAuthor: Gippeto » Wed Jan 03, 2018 12:30 pm

I swear...anything marked "Crosman" is laced with something...things are addictive. :lol:

A great many folks take rough MK1's and fit longer/better barrels....the ubiquitous "LD" configuration....guilty of this myself. Cut down and fit a barrel from an HW100...still need to test it. Tensioned barrels inside a full diameter shroud look pretty sweet too. :)

Believe I've seen that grenade cartridge posted before, still like the idea. Have not seen one in person, but seem to trigger very easily in the couple videos I've watched. Seeing it, and more so your version is sparking ideas....I see an afternoon with CAD coming up.

QDV based spool...couple thoughts.

Relying on momentum/inertia of components to delay ejection....looks like cart will start firing before it fully seats....API blow back concept??

I admit I'm curious to see how well it works in this case. :)

Going to use a spring to reset the spool, or reduce the opening to the back "store" some pressure during the shot cycle and use that to do the job?

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Re: preloaded pneumatic cartridge

Unread postAuthor: hectmarr » Wed Jan 03, 2018 3:22 pm

Interesting project Jack. I'd like to see shoot something like that. I had thought about making an air cartridge, at 120 psi, to shoot steel balls 1/4 ", something similar to what you drew but simpler, this way I have possibilities to build. I hope to see the progress of this theme. :)
I think that the percussion system moves the entire cartridge against the barrel that is fixed in relation to the body of the weapon. Where it is loaded, it is fired.
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Re: preloaded pneumatic cartridge

Unread postAuthor: jackssmirkingrevenge » Thu Jan 04, 2018 6:51 am

Gippeto wrote:I swear...anything marked "Crosman" is laced with something...things are addictive. :lol:


I have no problem believing that! I actually have two MK1s :oops: an older one in firing condition and a mostly complete bag of parts slated for Rugerification.

A great many folks take rough MK1's and fit longer/better barrels....the ubiquitous "LD" configuration....guilty of this myself. Cut down and fit a barrel from an HW100...still need to test it. Tensioned barrels inside a full diameter shroud look pretty sweet too. :)


This is more or less the plan, since it's .22 though it's on the back burner since I'm more enamored with bigger bores at the moment.

Believe I've seen that grenade cartridge posted before, still like the idea. Have not seen one in person, but seem to trigger very easily in the couple videos I've watched. Seeing it, and more so your version is sparking ideas....I see an afternoon with CAD coming up.


Note that there are two major variations, some with a central chamber in the "shell" portion (you can tell because the fill valve is on the nose) and others with a chamber in the "cartridge" portion (fill valve in the base). In the latter, the piston is somewhat balanced out so it's relatively easy to actuate even at CO2 pressures. Indeed in airsoft grenade launchers, you generally don't have a spring-loaded firing pin, the trigger just pushes directly on the base of the cartridge. I might have a few in the scrap box if you want to mess around.

Relying on momentum/inertia of components to delay ejection....looks like cart will start firing before it fully seats....API blow back concept??

I admit I'm curious to see how well it works in this case. :)


Herr Reinhold Becker would back me up :D

Image

If it works for a 20mm cannon it should work for a pneumatic cartridge, right?

Going to use a spring to reset the spool, or reduce the opening to the back "store" some pressure during the shot cycle and use that to do the job?


I was thinking of resetting it manually, any form of automatic reset is going to increase the force needed to open it anyway.

I still have my reservations about the design in terms of friction, the bigger the o-ring then the bigger the force needed to move it and it's proportional to the pressure. A paintball slide check for example at 850 psi is pretty stiff and I want to go well beyond that. Maybe a smaller diameter ported tube like the Magnum Air Cartridge is a better idea.

hectmarr wrote:I think that the percussion system moves the entire cartridge against the barrel that is fixed in relation to the body of the weapon. Where it is loaded, it is fired.


This design is basically what was patented by Michael Saxby.

Image

I think it's fine for lower pressures in the 150 psi region but the force holding the valve shut is proportional to the pressure in the chamber so for high pressures it would need a very strong hammer spring.
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Re: preloaded pneumatic cartridge

Unread postAuthor: Gippeto » Thu Jan 04, 2018 8:46 am

jackssmirkingrevenge wrote:Herr Reinhold Becker would back me up :D

I still have my reservations about the design in terms of friction, the bigger the o-ring then the bigger the force needed to move it and it's proportional to the pressure. A paintball slide check for example at 850 psi is pretty stiff and I want to go well beyond that. Maybe a smaller diameter ported tube like the Magnum Air Cartridge is a better idea.


Think the chief advantage here would be the reduced requirement for bolt mass..good enough reason IMO.

Friction is going to be an issue, and one of the reasons I'm liking the other cartridge you drew up. :) Better design than the MAC carts too...IMO.
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Re: preloaded pneumatic cartridge

Unread postAuthor: hectmarr » Thu Jan 04, 2018 9:23 am

Well, it's important for me to know in advance that it works. :bounce: I had no idea that this air cartridge mode was tested. I thought unnecessarily for not knowing this information .. :roll: I thought about building it to shoot at low pressure shot by shot, something simple. My home compressor has 120 psi maximum pressure, it is what it is.
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Re: preloaded pneumatic cartridge

Unread postAuthor: jackssmirkingrevenge » Fri Jan 05, 2018 5:15 am

Gippeto wrote:Friction is going to be an issue, and one of the reasons I'm liking the other cartridge you drew up. :) Better design than the MAC carts too...IMO.


I agree that the ball-locked ( :roll: ) design is generally better - if the spool o-ring diameters are close, it takes minimal effort to open, and it's basically an exhaust valve with zero piloting time - but it's certainly a more complex design to manufacture in quantity. That being said, the cartridges are too big to have it magazine fed as a "pistol" configuration, since they will be about the size of magnum 12 gauge cartridges so traditionally a one shot affair:

Image

I'm pretty sure I could get the cartridge to eject though, which will be a nice touch :)

hectmarr wrote:I had no idea that this air cartridge mode was tested


It was developed into a practical single shot rifle manufactured in limited quantities, the Saxby & Palmer Ensign. Here is one with cartridges and pump, quite an elegant design:

Image

The design really is quite simple, an inline hammer valve with a single seal for both firing and filling. I believe velocities of up to 800 feet per second were possible with these cartridges, no idea what the internal pressures were but I doubt they were as high as the 3000 or so psi one would find in a typical precharged pneumatic rifle.

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Re: preloaded pneumatic cartridge

Unread postAuthor: hectmarr » Fri Jan 05, 2018 6:02 am

A beautiful rifle, no doubt. I wish I could see one up close but they do not exist around here.
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Re: preloaded pneumatic cartridge

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Re: preloaded pneumatic cartridge

Unread postAuthor: jackssmirkingrevenge » Tue Jan 09, 2018 6:21 am

Alternative ball-locked configuration with an annular collar instead of a central firing pin:

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Re: preloaded pneumatic cartridge

Unread postAuthor: jackssmirkingrevenge » Tue Aug 21, 2018 6:04 am

Another possible configuration using a diaphragm valve in lieu of the piston, in the interest of simplicity.

Image

Because of the stress on the diaphragm, the valve seat has to be kept small in order to avoid it rupturing with the high pressure required for decent performance.

At those pressures I'm confident that an MP 18 style blowback mechanism would be feasible...

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Re: preloaded pneumatic cartridge

Unread postAuthor: hectmarr » Tue Aug 21, 2018 8:23 am

It looks interesting to use a resistant diaphragm. The recoil will be the product of the expelled mass flow and its speed, surely it should be more than enough to eject and load the new cartridge.
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Re: preloaded pneumatic cartridge

Unread postAuthor: Cthulhu » Wed Nov 07, 2018 12:56 am

I'm stuck at college but when I get home for the winter I'm going to try to make one of your original ideas out of brass.
I rendered a rough animation to help myself visualize the parts I need to turn.

Do you think that an 80mm diameter cartridge could still be piloted by a schrader valve?
At 500 psi GGDT is giving me almost 600 fps!
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Re: preloaded pneumatic cartridge

Unread postAuthor: jackssmirkingrevenge » Wed Nov 07, 2018 9:30 am

Sweet animation :)

Do you think that an 80mm diameter cartridge could still be piloted by a schrader valve?


If your piston is airtight in the direction from chamber to pilot, then it will work. The question is, how well? A pilot with better flow is definitely going to give you significantly faster opening time.
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Re: preloaded pneumatic cartridge

Unread postAuthor: Cthulhu » Wed Nov 07, 2018 1:47 pm

jackssmirkingrevenge wrote:Sweet animation :)

Thanks!
I just realized I wrote 80mm instead of 80 caliber (20mm) :oops: . I'm guessing the schrader should be fine then.
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Re: preloaded pneumatic cartridge

Unread postAuthor: jackssmirkingrevenge » Wed Nov 07, 2018 3:17 pm

Sure, I used a schrader valve for this one with a 25mm piston and it worked great: pneumatic-cannon-database/topic7173.html
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