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Semi Auto,Hopper Feeder=work or double feed?

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Semi Auto,Hopper Feeder=work or double feed?

Unread postAuthor: django » Sun Dec 27, 2009 6:16 am

Just saw this the other day,someone provided a link to it on another thread http://barragebarrel.com/index.php?main ... &chapter=0

Was thinking of making one similar?,surely this would double feed though woudnt it? ,was going to use the QEV+ Poppet Valve set up as per my Pitbull 9 Semi Auto http://www.spudfiles.com/forums/viewtop ... tml#247309 but use this feeder set up so I can get more ammo onboard and run more pressure! the Pitbull 9 can only take 110 psi before it double feeds as the Detent cant hold the bbs back!?......
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 27, 2009 6:31 am

Very interesting find! The ball detent is certainly familiar :) as to hopper, I had done some experimentation with something very similar here.

Here it is with the hopper and BBs as ammo, not 100% reliable but good enough. Note how the rate of fire decreases progressively as the pressure in the compressor goes down. Target was a plastic box.

[youtube]http://www.youtube.com/watch?v=hXM-bPOtJGU&feature=channel[/youtube]


Here's the hopper and valve firing:

[youtube]http://www.youtube.com/watch?v=U_1cN7lhW5c[/youtube]

On semi-auto it should work reasonably well.
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Unread postAuthor: django » Sun Dec 27, 2009 6:43 am

Well I might give a go but I think it will double feed like my 9mm semi,its odd as it double feeds over 110 psi so you wind more tension on the detent spring/screw more and more,it still double feeds if you wind it in more it then wont push the bbs past the detent! theres no inbetween? it double feeds or doesnt fire one or the other?.

if I make another gun I want another semi( 6mm this time) but if I cant run more than 110psi reliably then I doubt I'll build it,dont know how I'll attatch the hopper to the barrel( with strength) if I go ahead with it?.....
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 27, 2009 9:02 am

I think the key to avoid double feeds is in the feeding tube to the breech.

Image

Note how the breech is fed by a tube the same size as the barrel, theoretically this means that the BB in the breech goes down the barrel while the next BB is pushed up into the magazine, this has the added benefit of agitating the BBs in the hopper and avoiding jams.
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Unread postAuthor: POLAND_SPUD » Sun Dec 27, 2009 9:37 am

@django
I think I get it now... it's due to venturi effect
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Last edited by POLAND_SPUD on Sun Dec 27, 2009 9:49 am, edited 1 time in total.
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Unread postAuthor: django » Sun Dec 27, 2009 9:45 am

yeh,I think as usual your on the money Jack!= the reasons I liked this design is because its relatively simple and yeh I thought the same thing in regards to the air agitating the bbs in the hopper but downside is your losing performance in that the hopper is filling with air too.Power thats going to the hopper instead of the barrel/BB and as the hopper empties would be more noticeable I suspect?......
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 27, 2009 9:55 am

POLAND_SPUD wrote:I think I get it now... it's due to venturi effect


Possibly the valve opening interval is too long.

downside is your losing performance in that the hopper is filling with air too


True, but the fact that you have a BB diameter tube going to the hopper resticts the amount of air that is lost. You could always have a spring loaded follower to restrict this loss, as on inline BBMGs.
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Unread postAuthor: POLAND_SPUD » Sun Dec 27, 2009 10:08 am

Possibly the valve opening interval is too long
or chamebr volume is too large... I've done some test and I just realized that to get venturi effect even with a standard T
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Unread postAuthor: psycix » Sun Dec 27, 2009 4:36 pm

I used a friction detent (bump of rubber in front of BB) and a tubemag once.
(maybe I should post this prototype...)

Result:
The pressure buildup to make the BB pass the detent did not only prevent double feeding, it caused all the ammo in the tubemag to be pushed back.
This greatly limits feeding rate with a gravity mag, and managed to destroy BB's inside a springloaded tubemag...
When I adjusted the detent for a lower resistance, it apparently had more venturi then backpressure and doublefeeded.
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