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Topic: Homemade Semi-Auto Idea. Plausible Or No?

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Unread postAuthor: Vudu » Thu Apr 02, 2009 2:23 pm

So would restriction or dead space be better?

I'm confused here as well. But I'm guessing it has something to do with not enough air. Or something..

Either way, I'm going to use 1 inch fittings, which leaves me with 3inches
cubed of dead space, but it's also giving me more flow, thusly increasing the range on my gun. Of course this is all theoretical based upon a program which only has a predetermined ammount of variables.

I guess I'll just have to live with it shooting hot. :P
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Unread postAuthor: Vudu » Thu Apr 02, 2009 10:53 pm

Okay, so update.

I intend to use a palmers brass barrel unless somebody can tell me another material to use as a barrel, so basically this is a calling out to all who have created pneumatic paintball guns in the past.

And considering I don't have the slightest clue how to work McMaster, due to it's programming being a douchebag, I would be willing to write up a parts list if someone could help me by providing parts numbers to all materials needed on McMaster. I know this seems like I want to be spoonfed, and to be honest, I do. I need help with McMaster.

Also, I have secided I will probably be using an air-powered blowback breech design. I can probably get a diagram up tomorrow fully explaining it, but here is the jist of how it works.

1. You pull trigger, opening valve, firing paintball.
2. Excess air leaves through 3 porting holes near the end of the barrel.
3. Excess air pushes back a piston, resulting in the breech being opened.
4. Piston reaches venting holes, releasing all excess air.
5. Spring pushes piston forward again, moving breech forward.
6. Gun is now ready to shoot again.
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 02, 2009 11:57 pm

Vudu wrote:1. You pull trigger, opening valve, firing paintball.
2. Excess air leaves through 3 porting holes near the end of the barrel.
3. Excess air pushes back a piston, resulting in the breech being opened.
4. Piston reaches venting holes, releasing all excess air.
5. Spring pushes piston forward again, moving breech forward.
6. Gun is now ready to shoot again.


I've never seen that system actually implemented on a spudgun before, though it's often discussed on the forum since it's what many automatic firearms use and some assume it can easily be translated to potato launchers. First grasp the 44,900psi pressure difference, then think about it ;)

Personally, unless you're using high pressure and a powerful valve, I don't see it working. I would consider the blow-forward valve which operates at the breech, where the blast of propelling gasses are at their strongest.
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Unread postAuthor: Vudu » Fri Apr 03, 2009 12:15 am

Well, according to GGDT, I have plenty of air blowing the projectile out my barrel, and I can only see turbulence and other unforseen harm coming from the excess air that would otherwise screw with my accuracy, and the blow-back valve is pretty direct, in relation to dead space, and I can see it working, to an extent.

Then again, I'm pretty new to the whole, high pressure and complexities thing, as I have just recently graduated up from Nerf. :oops:

I will be trying to make the breech loose yet airtight (Courtesy of lubed O-Rings) , allowing for a weak spring, overall allowing for weak pressures to ready the gun.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 03, 2009 12:40 am

What pressure does GGDT predict you'll have in your barrel when the projectile is at the muzzle?
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Unread postAuthor: Vudu » Fri Apr 03, 2009 12:42 am

452 FPS.

But it says something 'bout how my barrel restricts flow, and with anything under 12 inches, the barrel is too short according to GGDT.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 03, 2009 12:54 am

Vudu wrote:452 FPS.


I asked what pressure, not velocity ;)

But it says something 'bout how my barrel restricts flow, and with anything under 12 inches, the barrel is too short according to GGDT.


If your valve is bigger than the barrel, then technically that's overkill, barrel restricting flow means you can afford to use a wider barrel. Overkill is good :)

Barrel too short means that at the point of projectile leaving the barrel, there is still a lot of air left so you can afford to make a longer barrel to exploit this (or make the chamber smaller)
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Unread postAuthor: Vudu » Fri Apr 03, 2009 12:58 am

Oops, aha. 60 p.s.i
Edit>> That's running off 100p.s.i, but I could easily amp it up to a max of 700 p.s.i; Actually, technically not true. I could only bring it to the pipings bursting pressure.

Barrel too short means that at the point of projectile leaving the barrel, there is still a lot of air left so you can afford to make a longer barrel to exploit this (or make the chamber smaller)


Or in my case, make it blow-black breeched! :P

But basically, I can make some large porting holes in the final 1 or 2 inches, and just run the piston, etc. off that.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 03, 2009 1:09 am

Vudu wrote:Or in my case, make it blow-black breeched! :P

But basically, I can make some large porting holes in the final 1 or 2 inches, and just run the piston, etc. off that.


If you pull it off, kudos to you :) remember though, low pressure means you'll need a large piston face to move your bolt effectively, and it can't be too heavy/have too much friction either.
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Unread postAuthor: Vudu » Fri Apr 03, 2009 1:12 am

I was thinking a rubber washer between two steel washers, maybe.. 1 inch diameter?

Or maybe a custom epoxy O-Ring head. Would that be more lightweight?
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 03, 2009 1:45 am

Vudu wrote:I was thinking a rubber washer between two steel washers


Assuming thin washers, it should be fine. I'd go with 1.5" though, that will give you 225% area (and therefore available force) over the 1".
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Unread postAuthor: Vudu » Fri Apr 03, 2009 1:54 am

Assuming thin washers, it should be fine. I'd go with 1.5" though, that will give you 225% area (and therefore available force) over the 1".



The washers are probably 1 mm, if not less, thick.

Alright, sounds like a plan. Now to do up a parts list, and figure out the labyrinth of which is McMaster-Carr..

And I'm still waiting on possible barrel materials. Does anyone know where I can acces lots of different paintball launchers, because searches didn't give me anything spectacular to read up on..

Edit>> So, about 15 pages into the search results, I found two topics which were actually helpful.. I think.

They both said their type of pipe was ideal for a paintball.
So here are the links. And below are the types of pipe recommended.

http://www.spudfiles.com/forums/duck-ta ... 17773.html

Recommends, sdr11 cpvc pipe, Haven't heard of it though.. French, is it?

And

http://www.spudfiles.com/forums/paintba ... 17624.html

And he recommends, Sch120 3/4" PVC, which I also have not heard nor seen of.

So.. Any help here?

Edit2>> Also, does anyone need a diagram of what my breech is goign to be rigged with?
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