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problem by designing shell ejection system

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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problem by designing shell ejection system

Unread postAuthor: nitrogigi » Thu Nov 15, 2012 8:40 am

Hi folks,
I'm actually designing an hybrid full automatic spudgun, where then chamber is a shell i've already designed, wich include ignition electrode, chamber, burst disk and the bullet (an airsoft aluminium BB)
my only problem is designing the extractor
does anyone already design a such thing?
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 15, 2012 9:55 am

If you make a simple blowback mechanism, all the extractor needs to be is a point which the base of the cartridge strikes, which tips it out of the extraction port.

[youtube]http://www.youtube.com/watch?v=HQ1I2hVTeWs[/youtube]
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Unread postAuthor: nitrogigi » Thu Nov 15, 2012 10:02 am

yes, but i want to reload automaticaly a new shell so, I though it has to be hold on the piston like on a real gun, could it work without being clipped on the piston?
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Unread postAuthor: pneumaticcannons » Thu Nov 15, 2012 10:06 am

copy cat!!!: http://www.spudfiles.com/forums/semi-au ... 24507.html
:lol:
jk

But seriously, you need to give us more details about your design. A diagram would help :wink:

In my design, I focused on keeping the rounds horizontal no matter what stage of the cycle it is in. It was a trade off with the ejection system complexity. Because I didn't want to deal with rounds chambering at all sorts of angles due to the physical size of the rounds and my facilities, I paid the price of a very complicated ejection mechanism. Although I have gotten the gun to successfully cycle single rounds consistently, If I could restart, and had adequate molding and/ or machining facilities, I would do away with the over-complicated ejection mechanism and replace it with a complicated inner geometry similar to that of a real firearm.

If your interested in my extractor, watch the video on the 9th post in the
linked thread. Simply a spring on the receiver end a magnet to pull the round the rest of the way.
Also check out some of JSR's work on blowback hybrids.

Edit: Crap, double ninja'd
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Unread postAuthor: nitrogigi » Thu Nov 15, 2012 10:25 am

my caliber is far smaller then this, I plan to shoot 6 mm aluminium airsoft balls

here's the shell some little things have been modified like the screws on the valve :
Image[/img]

if you need translation or explanation

the shell would be 14mm of diameter and 75mm long
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Unread postAuthor: nitrogigi » Thu Nov 15, 2012 2:41 pm

Here you've got the first images from the 3D model:

Image
in firing position

Image
in ejecting position

Image
view on the piston with the magnet (in grey) making electric contact with the shell for the ignition and in case of misfire, to extract the shell
and in black, the key for the ejection of the shell
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 15, 2012 3:38 pm

That's quite a complex shell.

Have a read through my extensive efforts in the field: http://www.spudfiles.com/forums/hybrid- ... 19504.html
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Unread postAuthor: nitrogigi » Thu Nov 15, 2012 4:26 pm

I like your cartridge, I like the system without burst disk, I think I'll keep the rear of my cartrige a bit modified, and take the front of your's, with a guiding cone to enter the barrel correctly, like on mine.

Let me do a bit of CATIA to arrange this
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Unread postAuthor: Zeus » Thu Nov 15, 2012 5:25 pm

Firearms use a rim or channel in the base of the case, a spring loaded extractor claw rides in that groove, the extractor is in line with the ejection port. The exjector is just a small nub that the shell hits, and it's opposite to the ejection port.

If you have a bolt action rifle to hand, use it as an example.
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Unread postAuthor: nitrogigi » Thu Nov 15, 2012 5:31 pm

yeah, I know how it's made, but it's far to complicated to built on a spud gun, it's what I wanted to make first, but at the end I don't really need an extractor claw, though, I'll use a kind of blow-back
(I'm french, having a rifle to hand legaly is far harder for us)
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Unread postAuthor: Zeus » Thu Nov 15, 2012 5:38 pm

Let me tell you, it's really easy. You'll still need an ejector, but with well lubricated shells, you should be right. Use a good engine oil for lubrication.

And check out Weaponsguild.com, it's the Spudfiles of firearms.
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Unread postAuthor: nitrogigi » Thu Nov 15, 2012 5:45 pm

I'll better use silicone oil or such and a low flamable oil than motor oil, 'cause my calculations said the shell could be heaten to 300°C after a shot at mix 10, and I'm scared with such a heat and a bit of flame when it blows back, motor oil could inflame
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Unread postAuthor: Zeus » Thu Nov 15, 2012 5:49 pm

I quench dull red steel in cheap used engine oil for case hardening, and I'm yet to have it do anything but smoke. Synthetic engine oil is perfect for your application.

I'll disassemble my .22 bolt for you later today, show you how simple it really is.
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Unread postAuthor: nitrogigi » Thu Nov 15, 2012 6:05 pm

thanks
my only problem with oiling is the conduction of electricity for the ignition spark
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Unread postAuthor: Zeus » Thu Nov 15, 2012 7:20 pm

Mix graphite powder with the oil, it'll help lubrication and make the oil conductive.
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