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Shell ejecting venturi gun

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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Shell ejecting venturi gun

Unread postAuthor: PVC Arsenal 17 » Wed Dec 24, 2008 2:18 pm

If you guys have seen any of my work, you know that I like simplicity and cleanliness.

Recently I started building a Semi Auto Nerf Gun. I'm still not done with it, though. I'm just that freakin lazy. I will finish it though.

But the progress I've made on it so far has already to proved that this design is too complex for my tastes. It's not anything that I'm incapable of building (although it may seem so because I haven't finished it yet) but there seems to be too much that could go wrong. (darts getting pinched, bolt getting stuck, cylinder rattling itself free of the barrel) I am absolutely OBSESSED with simplicity and reliability so I've started designing an even more simple gun. Here's a quick diagram I made and I'll give a little explanation as to how it will hopefully work.

Image


There will be a spring loaded magazine set inline with the barrel. Within it will be shells containing lightweight* nerf darts. Each shell will be closed at the back.

There will be an opening cut into the barrel where the shell ready to be fired is located.

Perpendicular to that shell is a subminiature cylinder (retracted)

Slightly in front of that shell will be an inlet into the barrel for a QEV.


Upon firing, the air flow from the QEV into the barrel will "suck" the dart down the barrel sort of like the Vogt Pattern. I've tried this and it does indeed work, especially because Nerf darts are so light. EDIT: I'M RETARDED AND I WAS THINKING OF SOMETHING DIFFERENT. PLEASE IGNORE MY STUPIDITY AND THIS WHOLE THREAD FOR THAT MATTER. The reason for having each shell closed at the back is to ensure that only one dart fires and not the whole row.

After the dart fires, the submini cylinder will extend and push the spent shell out of the ejection hole. When the cylinder returns, spring pressure on the row of shells pushes a new one into position.

I will have to coordinate that QEV and the cylinder somehow... but that'll come later. Any comments/suggestions?
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Last edited by PVC Arsenal 17 on Sat Dec 27, 2008 12:42 am, edited 2 times in total.

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Unread postAuthor: Eddbot » Wed Dec 24, 2008 2:31 pm

I like it, seems simple enough, but it kinda limits projectiles to nerf darts and lightweight stuff.
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Unread postAuthor: PVC Arsenal 17 » Wed Dec 24, 2008 2:38 pm

That's all I plan on shooting so it works for me!
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Unread postAuthor: Hubb » Wed Dec 24, 2008 2:39 pm

I asked about the Vogt pattern not too long ago, and this was the reason why; to construct a Nerf gun.

I am a bit confused on your ejection system, though. Will it automatically eject, or manual? Other than that, it is as you wished; very simple. I also believe that, if you get it to work, it will be one of the nicer Nerf launchers.
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Unread postAuthor: PVC Arsenal 17 » Wed Dec 24, 2008 2:47 pm

It will eject automatically. Firing will be semiautomatic, though.
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Unread postAuthor: Hubb » Wed Dec 24, 2008 2:54 pm

Just a thought but if you make the ejection port large enough and just right, the vacuum created from the shot may pull the shell out.

In theory, this would suck the dart and the shell up (assuming you have a shell catch). A small ramp is placed in the right part of the launcher and the dart will continue down the barrel, while the shell hits the ramp and ejects. Your spring will then set the next shell to be fired.
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Unread postAuthor: MaxuS the 2nd » Wed Dec 24, 2008 3:34 pm

Spring-fed magazines are a Pig. You'll find this out when you come to make it.
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Unread postAuthor: PVC Arsenal 17 » Wed Dec 24, 2008 3:42 pm

Trust me I already know... This one won't exactly have a magazine. The tube containing all the shells will be fixed to the gun. To reload you will take a cap off the back. The spring will be connected to the cap for convenience. Just pop in the shells and screw the cap back on.
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Unread postAuthor: skyjive » Wed Dec 24, 2008 4:03 pm

I like the design, its very creative. Two thoughts: if the friction between bullet and shell is greater than that between shell and barrel then the shell will also be sucked forward a bit and disalign from the ejection port. Also, since you have a nose-to-tail magazine setup, your capacity will be quite limited unless you have a very long tube as a magazine.
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Unread postAuthor: PVC Arsenal 17 » Wed Dec 24, 2008 4:11 pm

The barrel will be of a smaller diameter than the tube that contains the shells. The shell will not be able to travel beyond that. I only plan on the gun having a capactiy of about 10 rounds. They will be fairly short too- between 1" and 1.5".
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Unread postAuthor: psycix » Thu Dec 25, 2008 7:48 am

One comment:
Why use shells? (Besides looking awesome in some way)

You could also do with without shells.
No ejecting needed.
If you are afraid that you may fire more then one at a time, simply use the pneumatic cylinder to block them off.
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Unread postAuthor: SP00K » Thu Dec 25, 2008 2:45 pm

absolutely OBSESSED with simplicity and reliability


Oiuf, welcome to my world. I have some pretty good ideas, but eventually, when I figure out how it WOULD work, it ends up being too complicated, too expensive, or I'm unable to build it because of a lack of tools.


Why use shells? (Besides looking awesome in some way)


It's the novelty that matters. The point of this gun was to use shells. Any joe shmoe can design a nerf gun.
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Unread postAuthor: POLAND_SPUD » Thu Dec 25, 2008 3:54 pm

I like the design and its ingenuity...

however I don't think it'll be easier to make than the aircylinder design, which is possibly the easiest way to achieve semiauto... my advice is - stick to it

since you decided to use foam darts and use shells it's going to be a little bit more challenging that it would be if you used spherical ammo but I am sure that you can find some way to make it work... you could try to make an ejector and base it on how real firearms work
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Unread postAuthor: PVC Arsenal 17 » Fri Dec 26, 2008 8:51 pm

Stupid me didn't realize that this concept doesn't work well (if at all) with cylindrical ammo. Back to the drawing board... Luckily I have another idea in mind.

DISREGARD THIS THREAD. I'M DUMB.
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Last edited by PVC Arsenal 17 on Sat Dec 27, 2008 12:43 am, edited 1 time in total.

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Unread postAuthor: Sticky_Tape » Fri Dec 26, 2008 10:27 pm

I don't even understand the concept I would think the airflow would push the dart into the shell not pull it out the barrel. But I understand air moving over a surface causes less pressure over said surface making the surface parallel have a force imparted on it hence sand blasters,vogt pattren,airfoils. but what the hell I don't think that would happen.
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