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Simplest Self Loading Semi Auto

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Simplest Self Loading Semi Auto

Unread postAuthor: phantomwarrior17 » Tue Oct 28, 2008 8:21 pm

I've been reading for the past couple of hours trying to figure out a good way to make a semi auto gun. So far I've come up with medicore results. The only thing that I have found is a QEV. My problem is that I want it to air seal like the air nozzle and tappet plate on an airsoft AEG. My idea is to make it bolt action for loading and make the firing mechanism semi auto but i can't figure out the firing mech. My idea is to use a blow gun to pump air into a reservor chamber until it blows a valve (forget the name but it blows it self after a certain PSI). Does anyone have any better ideas along the lines of true semi auto. Thanks. If not just as semi auto firing with out the air nozzle.
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Unread postAuthor: starman » Tue Oct 28, 2008 8:38 pm

No proper semi-auto is going to be simple in the simple sense. Have you taken a look at Clide's GB semi?
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Re: Simplest Self Loading Semi Auto

Unread postAuthor: judgment_arms » Tue Oct 28, 2008 8:43 pm

phantomwarrior17 wrote:forget the name but it blows it self after a certain PSI

burst disk. :wink:

and somebody will beat me to that... :roll:

as for semi-auto cycling, simplest, by far, is an Autococker type mechanism.

Image

basically, pull the trigger and it fires the gun, continue pulling and it throws a switch that opens the bolt, release the trigger and the switch gets flipped back and bolt closes.

after that is a blow-forward bolt, fallowed by blow-back.
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Unread postAuthor: Lentamentalisk » Tue Oct 28, 2008 8:51 pm

Phantom: I hope you are not referring to a burst disk, as that must be replaced every time. I think you are referring to a popoff valve. The problem is that that will waste lots of air, and not vent to well. Look around on the site, and you will see that few have attempted semi-auto because it is just too damn complicated. Look at what has been done, and then think up some ideas, and give us a diagram.
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Unread postAuthor: judgment_arms » Tue Oct 28, 2008 9:38 pm

Lentamentalisk wrote:Phantom: I hope you are not referring to a burst disk, as that must be replaced every time. I think you are referring to a popoff valve.

*facepalm*
now why didn't I think of a pop-off, that would have been the logical choice. :oops: :roll:
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Re: Simplest Self Loading Semi Auto

Unread postAuthor: jackssmirkingrevenge » Tue Oct 28, 2008 10:59 pm

phantomwarrior17 wrote:My idea is to use a blow gun to pump air into a reservor chamber until it blows a valve (forget the name but it blows it self after a certain PSI).


Look at this discussion, there is a way in which you can combine the conceptual workings of the pop-off valve with a blow-forward breech, that will give you both a firing valve and reloading mechanism.

Image

For semi-auto, all you have to do is remove the green component and replace it with a blowgun valve, like so:
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Unread postAuthor: phantomwarrior17 » Wed Oct 29, 2008 4:59 pm

Thanks jackssmirkingrevenge that was exactly what I was just about to draw, but you beat me to it and made it better. Mine is the way with the blow gun. See the problem that I have is that I wanted my semi auto to be crisp and only use a certain amount of gas so as not to waste air. So what I don't understand is how clide's bottom valve works. That would definitely give me the crispness I want. This one:

http://gbcannon.com/pics/GBSemi/gbsemi.gif

Since the air pressure is holding the farthest front one closed, how does it open when you release the sear. Does the air want to ge left so it releases the sear so when the other side empties it repressurizes it because that is the low pressure. Is that correct?

Is this the simplest crisp blowback all of you guys have heard of?

Also, I won't need a reserver with clide's design since I'm firing bb's correct. I don't have to move a lot of air then to fire if I understand correctly because I'm moving a low mass object. Thanks. I'll try to attempt the first part this weekend with my broken m4 airsoft gun becausue I can use the magwell from it and the hop up unit and the air seal nozzle along with the piston.
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Last edited by phantomwarrior17 on Wed Oct 29, 2008 5:27 pm, edited 1 time in total.

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Unread postAuthor: jackssmirkingrevenge » Wed Oct 29, 2008 5:21 pm

In clide's design, the left end of the piston is slightly larger than the right end. This means that the pressure difference induces a force to the left, so it is the sear that keeps the valve shut. Once the sear is released, the piston is free to move.

What exactly do you mean by "crisp"? Short lock time from trigger to shot? The design I suggested would not waste air because it will only fire when the fixed chamber volume reaches a fixed pressure, and your natural instinct will be to release the trigger when it fires.

Have you looked up ant's hammer designs? They would probably give sort of air efficiency and firearm-like trigger you seem to want to achieve, though perhaps it would be lower on power. I'm assuming you were thinking of an airsoft calibre?

edit: for airsoft, I would just hook your magazine directly to a blowgun like so, or if you want a blow-forward bolt, make something like this.
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Unread postAuthor: phantomwarrior17 » Thu Oct 30, 2008 2:17 pm

Yes your second idea from the edit is exactly what I was gonna do except different. I'm going to use the stock piston head and cylinder and allow the air to travel out side the cylinder instead of through the piston. Have pics up a little later if you don't understand. The air nozzle will just be an old barrel that will seal to an old hop up unit from my m4.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 30, 2008 2:39 pm

phantomwarrior17 wrote:Yes your second idea from the edit is exactly what I was gonna do except different.


What kind of hellish quiz is this? :D

Have pics up a little later if you don't understand.


Better ;)
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Unread postAuthor: Ragnarok » Thu Oct 30, 2008 4:21 pm

jackssmirkingrevenge wrote:What kind of hellish quiz is this?

Schrödinger's quiz, where any answer is right and wrong at the same time! :D

So, having said that, now I'm in Schrödinger's humour, where it's only funny because it isn't. :roll:
And for my final trick, the true Schrödinger joke that is 50% funny as long as it's unobserved:


Sorry, I'm indulging in quantum physics humour, I'll go now.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 30, 2008 4:29 pm

Big Bang Theory is one of your favourite shows, right :D You're easily a UK variation of Sheldon, and I mean that as a compliment hehe
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Unread postAuthor: Ragnarok » Thu Oct 30, 2008 4:41 pm

EDIT: Ignore me, Wikipedia made it obvious. It's not a show I watch.
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Unread postAuthor: phantomwarrior17 » Thu Oct 30, 2008 5:43 pm

You animation before you showed it with a photoshoped blowgun could be adapted with a blowgun which could give me the crisp semi auto I want. Just add a chamber behind it and make the valve infront of the cylinder with an extended middle rod.

Either way here are my pics made very sloppy without some of the orings in some needed places:

Image

and firing

Image
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 31, 2008 3:47 am

Used in conjunction with an airtsoft magazine/hop-up unit and built a little less sloppily than it was drawn, that should work well :)
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