Pneumatic shells

[Sticky_Tape]

After reading a few posts I have decided to scetch up plans for a pneumatic shell. it uses a shrader to vent the pilot chamber but somthing good about this is that instead of a co-Axial where the barrel is in the chamber the barrel starts on the front of the chamber. This gives more area inside the chamber for air giving the ability to have a longer barrel and more volocity. It also has a piston support to have the piston seal the barrel. critisize it if you like.

[VH_man]

I like it. I think JSR has done something along these lines, except his had far more dead space.

If you construct it, Please post them and the gun that uses them..... PWEEZ......

[Tom]

It looks good but you van do it much simpler. Don´t use a shrader to activate the cartridge use a hammer. That is less work and you can always finetune your hammer and spring!!!. Or maybe a brustdisc is a idea in combination with a hammer(again ).
GR.Tom

[Sticky_Tape]

I don't know exactly how I'm going to make this but if anybody wants to use this idea they can. And how many projects does JSR have it seem every time that someone comes up witha new Idea JSR has already done it or was planning on it like that airsoft crossbow. Well anyway I might make a single shot gun like a pop-shot mini but a little bigger. Maybe the size of a luger.

[Sticky_Tape]

I'm a bit of a noob so what is a hammer?

[windshrike]

Wow, I haven't posted in a while. This is a good idea, spudchucker, essentially the HEAR valve in a cartridge. However, you'd need fairly high pressures to get a 0.177-0.25 caliber round to a good velocity. Well, I'm guessing that airgun pellets are your ammunition of choice, as per the schematic.

@Tom: I think that he meant that a hammer be used to hit the pin in the schrader, mimicking a firearm's action, venting the pilot, and firing the round.

EDIT: Spudchucker, you know how in a firearm a hammer strikes the firing pin to discharge? The same concept.

[Sticky_Tape]

Oooo, I thought that he meant a special valve in the shell. Yes I know how a hammer hits the pin to discharge.

[Antonio]

How do u charge the main chamber with air?

[frogy]

Lol ant... THE SCHRADER...

This is a fairly common pneumatic design. It's basically a coaxial barrel sealing valve... Well not quite common, but many people have posted concepts of it. It's fairly easy to make with proper tools for forming\molding a piston.

I believe a few of JSR's designs use a similar concept.


It would be easier if you used a coupling and a bushing instead of a reducer... Are reducers even pressure rated?

You should have both ends of the piston (sealing face\front) and (rear seal) as full size, but drill\cut holes in the front piston nearly everywhere, but the sealing face, remembering to keep enough plastic\epoxy on the front piston so it doesn't shatter...

A female adapter may be even better, with a threaded bushing (Chamber Thread x Slip barrel) so you can remove the piston if you have any problems...

The best way to assemble the rear bumper would be to drill and tap for the 1/8" Schrader, thread in the Schrader and epoxy it in... Then the harder part...

Either dry fit in a small piece of pipe that fits in the end cap and then pour in foam\silicon or similar for the bumper, or glue in a small piece of pipe with the open end large enough to fit fully into a coupling, then pour in the foam\silicon bumper.

The problem about the first option, is that later you will have to apply the primer\glue with a cotton swab or something... The downside of the later is that you will have to buy an extra coupler, but this could make it harder to fit the piston in...

Enough rambling for me

[Sticky_Tape]

I think I will make it out of 3/4'' copper tube it seems like you were making it sound like I was going to use pvc or cpvc pipe.

[Sticky_Tape]

You should have both ends of the piston (sealing face\front) and (rear seal) as full size, but drill\cut holes in the front piston nearly everywhere, but the sealing face, remembering to keep enough plastic\epoxy on the front piston so it doesn't shatter...

I might try that frogy

[Antonio]

Lol ant... THE SCHRADER...

I dont get how the air from the schrader valve goes past the piston to the main chamber. If it would leak past the piston then when the schrader is fired it would leak too much past it right. I am not sure if the drawing lacks some details or if I just dont get it.
thnx

[frogy]

Ya, that's a "problem" about a Schrader as a pilot valve...

You can either tap a expensive (and stupid idea) one-way valve into the rear piston, make a one way valve yourself (hard with a 2 piece non-coaxial piston) or have 2 schraders... One for the fill valve and one for the pilot...

The easiest thing to do would be to have the piston barely move at all when it seals, and have a tightly fitting rear piston, so when you fill it will fill the chamber, the piston only moves about 1mm or so forward to seal, and when you piston the chamber, it only has to move about 1mm back...

A very stupid thing I wasn't thinking about earlier, is that the air is just going to escape around your front seal when your firing, unless you have some type of fill system that has the whole piston move forward before it starts to fill the gun... I'll go grab one of JSR's concepts that uses this design...

Actually you just wait for JSR he's got too many post to search through.

[Sticky_Tape]

Now I discovered a new problem. How do I take the pump off the shell without venting the piston? I heard of JSR's teqnique of useing a shock pump with the o ring in the attachment but unfortunatly I don't have a shock pump

[jackssmirkingrevenge]

unfortunatly I don't have a shock pump

If you want good performance from a small shell volume then you'd better get one

this is the design that was mentioned, and here you'll find the cartridge that I made.

I shelved the project however as cartridges would be too complex to manufacture in quantity, plus the piston mechanism adds weight. Personally I think there's more promise to be found in burst disk cartridges..

I dont get how the air from the schrader valve goes past the piston to the main chamber. If it would leak past the piston then when the schrader is fired it would leak too much past it right. I am not sure if the drawing lacks some details or if I just dont get it.
thnx

Ant, this is how most piston valves work - as you're filling from behind, air leaks past the piston to pressurise the main chamber. For the piston to work however, your pilot valve (in this case the schrader" needs to have a greater flow than the leak around this piston, this means the pilot chamber empties at a rate quicker than it's being filled, so it's pushed back by the pressure difference.