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How does this semi-auto gun work?

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How does this semi-auto gun work?

Unread postAuthor: auxiliary » Tue Jul 29, 2008 10:32 am

I'm sure that many of you have seen this video:
[youtube]http://youtube.com/watch?v=AT2en097DL4[/youtube]
All I can see from the video is that he uses a QEV and a blowgun, but I can't figure out what that thing is that's poking out of the brass fitting behind the blowgun. Is it a pop off valve? Does anybody know how this operation works? This is one the the most effective and simple semi-auto designs I've seen.
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Unread postAuthor: Mr.Sandman » Tue Jul 29, 2008 10:55 am

ive seen that befor too im pretty sure the chamber fills up then he releases the air and it fills up again or it just uses a hammer valve. but you can clearly see the air line in the background


Edit: the valve behind the qev is a quick disconnect valve that most standard air compreesors use
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Unread postAuthor: auxiliary » Tue Jul 29, 2008 11:12 am

So the way it works is the air from the compressor goes past the blowgun and through the QEV into the chamber below the barrel. Then when the blowgun is actuated, it pilots the QEV releasing the air in the chamber below the barrel. Correct? If it is, then how is it that the compressor hose fills up the chamber so fast? And why doesn't the blowgun release air that is coming from the compressor and just pilots?
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Unread postAuthor: Mr.Sandman » Tue Jul 29, 2008 11:15 am

well that is how it works. but the way the compressor fills it so fast is that he is probably using the air tank and when the air tank runs out the compressor turns back on to charge up the air tank.and the reason the blowgun dosent just use the air from the compressor is because the air flows into the chamber and not the blowgun
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Unread postAuthor: Carlman » Tue Jul 29, 2008 11:41 am

mrsandman, what he is trying to say is why does the blowgun pilot the valve when it can more easily just vent out the incoming air line.
what i want to know is how in gods name did he make his mag feeding work :shock:

EDIT: whoops forgot to answer question :roll:

he has a ballvalve that he closes just enough to get a good tradeoff with piloting time and fill time.


anyone with ideas on the mag?
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Unread postAuthor: blind909 » Tue Jul 29, 2008 11:58 am

It is an air compressor, You can hear it towards the end.
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Unread postAuthor: Carlman » Tue Jul 29, 2008 12:01 pm

i gathered that part
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 29, 2008 12:02 pm

Interesting how (assuming normal compressor pressures of around 100 psi) it doesn't appear to be very powerful, in spite of the oversized QEV, which implies that the piloting is only slightly better than the filling air as the piston/diaphragm doesn't actually open much.

As to the magazine, the mechanism appears to be hidden so it could be anything from a blow forward bolt to a simple tee fitting with an o-ring seal.
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Unread postAuthor: POLAND_SPUD » Tue Jul 29, 2008 12:08 pm

there is something behind the T (the one with a blowgun)... it may be a BV (or something else... )
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Unread postAuthor: Carlman » Tue Jul 29, 2008 12:08 pm

its at 40 psi it says so if you go to it in youtube so that explains the power

ive messaged the guy with a nice long kind as can be message as to his loading mechanism

POLAND_SPUD wrote:there is something behind the T (the one with a blowgun)... it may be a BV (or something else... )


i mentioned that above but no harm

any idea as to loading?
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Unread postAuthor: POLAND_SPUD » Tue Jul 29, 2008 12:24 pm

it seems to me that there is no bolt becasue the magazine tube has an endcap or something

you know what I mean? - it's ment to be airtight

so most likely it's
a simple tee fitting with an o-ring seal
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Unread postAuthor: Carlman » Tue Jul 29, 2008 12:25 pm

how does such o ring setup work>?

never actually heard of it before
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 29, 2008 12:31 pm

POLAND_SPUD wrote:it seems to me that there is no bolt becasue the magazine tube has an endcap or something

you know what I mean? - it's meant to be airtight


Not necessarily - with my blow-forward semi, some air would leak into the mag and it would blow the BBs out if it didn't have a heavy cap on it.

how does such o-ring setup work


I have a diagram somewhere, basically you have a tee and a magazine that's the same tube as the barrel, when the valve opens the BB in the barrel is held against the o-ring until it fires, in the meantime little air is lost through the mag because the BBs there are a close fit to the tube. These BBs get pushed up the mag, meaning you only fire one shot at a time.
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Unread postAuthor: Carlman » Tue Jul 29, 2008 12:39 pm

wish someone brought that idea up when i asked for bb mag ideas :roll: :D

so if i had a 1/4" brass male T and i cut a slot just after the middle threaded bit and slipped an o ring on it so it created like a hopup type use aswell would that work?

and if it doesnt i could cut two slots (one up and one on the bottom) to hold it more

How reliable is this method of feeding?
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 29, 2008 12:58 pm

The important thing is that the BB close to the barrel is actually partially in the barrel, so it can only be blown out, while the BBs following in the mag are actually in the mag tube, so they can only be blown down the tube, as opposed to down the barrel to give you burst fire. The spring must be strong enough to push the BBs down but weak enough to allow the BBs to be pushed back by the pressure.

There were a couple of diagrams here but the links are long dead, I have one on my PC but that's currently many kilometres away.

Assuming spherical projectiles that are a good fit in the tube you're using as a magazine, and a spring of the correct strength, this should be a very reliable setup.
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