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Cartridge Powered Air Rifle Ideas

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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Unread postAuthor: jackssmirkingrevenge » Sat Nov 26, 2011 12:34 am

DerpWithAGun wrote:It would be cool to use the same dimensions of the 12 Gauge shell and .308 round to build these airgun cartridges. (I hope it isn't banned to talk about firearm shells).


*cough*

Image

Image

Made without the benefit of a lathe.

Seriously, read through that thread, it will answer a lot of questions.
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Unread postAuthor: DerpWithAGun » Sat Nov 26, 2011 1:46 am

Wow that's really cool!
I've drawn up my final designs. Tell me if anything should be changed to make it work better.

Image

Black = Main cartridge
Grey = End plugs
Gold = Schrader Valve
Blue = Piston
Brown = sealing face

To me it looks good. It probably might need a little work on the piston to make it move better but I'm happy with this. All end plugs and the schrader valve will be epoxied into place. The picture here is actually my design for my shotgun version. This cartridge is the same size as a 12 Gauge shell which is 7cm long and 2cm in diameter. The rifle cartridge will look the same as that but it will only be 4cm long, 2cm in diameter but it will have less pressure and the barrel will be 5mm. The shotgun will have a 1 or 1.5cm diameter barrel.

The shotgun cartridge will take 1000 psi and the rifle will take 800 psi.
Tell me what you think guys! :)
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Unread postAuthor: jackssmirkingrevenge » Sat Nov 26, 2011 2:20 am

That looks like it would work well.

You could mod it slightly as attached in order for the schrader to not be so exposed.

Don't cut from the schrader threaded part, otherwise it won't seal against the pump attachment.
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Unread postAuthor: DerpWithAGun » Sat Nov 26, 2011 2:49 am

Thanks Jack, I might put the schrader like that but in real life that will be quite small and I don't think the pump's hose will fit in that gap.

On the piston I might make it thicker on the outside so the piston wont flip because it's so thin. Making it thicker on the outside and making the sealing face stay thin it will add stability the the piston might even glide more smoothly.

One last question, it is possible to buy schrader valves from hardware stores just on their own? Or do I have to buy a whole bike inner tube each time and then cut the schrader off?

I am so excited to build this. Sadly, I have to wait until Christmas before I actually get my lathe and mill :(

Will be building a bolt action rifle, a Lever action shotgun and a pen-gun. :)

Thanks to everyone who has helped me!
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Unread postAuthor: Hawkeye » Sat Nov 26, 2011 10:11 am

You can salvage schrader valves from the old tubes that bike shops throw out.
The schrader as Jack shows it should still be able to accept the pump head. Shock pumps have a thread on attachment rather than regular type with the bulky lever attachment.
You can buy larger schrader valves on their own for use on water tanks but they have a larger thread on the other end. Either 1/8 or 1/4. At least where I live.
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Unread postAuthor: Brian the brain » Sat Nov 26, 2011 12:49 pm

a Lever action shotgun


I'll be keeping a close eye then
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: Gippeto » Sat Nov 26, 2011 12:54 pm

Tire shops are another source of free schraders...they change them out when installing new tires.

The plumbing schraders are called snifter valves...very common.

And...Welcome back Hawkeye. :)
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Unread postAuthor: DerpWithAGun » Sun Nov 27, 2011 3:31 am

Hey Guys,

I was working on my accurate drawings of my plans for the shotshell cartridge. (I have decided to make a lever action shotgun first.) I have come across a problem. My shotshell dimensions is 61mm x 24mm. The end plug that houses the schrader valve is 20mm long. The end plug for the barrel is 10mm long. The barrel is 30mm long and 10mm diameter.
I have gone with the design where the schrader valve is hidden inside end plug (JSR's modification to my original cartridge.). Behind the piston there is a 5mm gap where pressure builds up. Infront of the piston is a 12mm gap.
The problem here is that there is barely any room at all for pressure to build. I don't want to decrease the barrel's diameter because my type of ammunition is buckshot. Which in this case is 12 bb's that are 3mm in diameter. I cannot decrease the length of the barrel because that would create more pressure behind the piston and less pressure in front of the piston which means that when I open the pilot valve, the piston will move backwards very slowly. Another problem is these are the dimensions of the cartridge WITHOUT the wall thickness drawn into the design.

So, would anyone be able to help me? I want to have 1000 psi in this cartridge. Do you think it will be able to propell 12 3mm Steel BBs at 300 fps? Lastly, what would be the recommended wall thickness if I want 1000 psi?

Thanks.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 27, 2011 3:44 am

DerpWithAGun wrote:I was working on my accurate drawings of my plans for the shotshell cartridge.


Let's see them :)

Do you think it will be able to propell 12 3mm Steel BBs at 300 fps?


With a dimensioned diagram we can do some GGDT modelling.

Lastly, what would be the recommended wall thickness if I want 1000 psi?


Depends on the material. A steel CO<sub>2</sub> capsule has a wall thickness of around 0.9mm and will happily hold 1000 psi safely.
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Unread postAuthor: DerpWithAGun » Sun Nov 27, 2011 3:54 am

Alright.
I was drawing my plans 1:1 scale on paper so let me go and get my laptop with the webcam and I'll upload it.

I put in all the info I knew onto GGDT and I got this:
Travel Time: 8.5 ms
Pressure Drop: 957.9 psi
Muzzle Energy: 0.3 ft*lb
Muzzle Velocity: 27 ft/s

I probably entered in some of the information wrong but I'm glad you can do it for me :)

Just give me one minute I'll get my laptop! :)

EDIT: Laptop is charging give me a few minutes :(
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Unread postAuthor: DerpWithAGun » Sun Nov 27, 2011 4:09 am

Okay, Here is the design! :D

Image

EDIT: Laptop was about to die I couldn't write anything else.
The parts that are clear white that don't have any pattern or shade on them are the areas where pressure can build. I forgot some dimensions; The piston is 13mm long. The gap where the piston meets the barrel is 4.5mm. The end plug on the right of the picture is 10mm wide.
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Unread postAuthor: pneumaticcannons » Sun Nov 27, 2011 5:23 am

hmm, seems like you right about it having practically no chamber volume... Even for 1000 psi thats pretty small... :? Are you sure you cant make it just a bit longer? That 27 f/s actually sounds about right.
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Unread postAuthor: DerpWithAGun » Sun Nov 27, 2011 5:37 am

Well I don't know. That is about the right size of a 12 gauge shotgun shell and I wanted to base my designs on that.
Since I'm building a lever action shotgun with this, increasing the size would cause many problems. I guess the lever action will just have to wait. I'll start designing my cartridge for the rifle tomorrow. That will be a lot easier. to make.

I'll just wait for JSR's response then I can decide and re-design my cartridges.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 27, 2011 5:38 am

Assuming a 20 inch barrel, 10mm calibre and an extremely thin barrel wall inside the cartridge (:roll:) for 2.5 grams of BBs and sabot I got around 500 fps, pretty healthy.
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Unread postAuthor: DerpWithAGun » Sun Nov 27, 2011 5:49 am

aha! So my design did work after all? but You said 2.5 grams of BBs. Try it with 10 grams. 12 BBs that are 3mm in diameter is roughly 10 grams. I might just increase the length of my cartridges by 10mm - 20mm just for a bit more power. Thanks a lot JSR! And 500 fps! That's heaps! I think I read on the Farco Air Shotgun website that the Farco got 300 fps.

Time to re-design my Shot-shell just a bit more and add final adjustments and then I'm ready to go!

Thanks again to everyone who has helped so far! :)
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