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Pulling vacuum @ the breech - Instrumentation artifact or real phenomenom?


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#1 Snipez4664

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Posted 20 November 2008 - 01:09 PM

Just check out the graphs at http://automags.org/...ead.php?t=34429

They all have a significant negative pressure occurring around the time of ball exit. You can also vacuum time cockers (I've seen some open bolt guns claim this also)

Some details on that:
Suction Timing- Now, many people are interested in suction timing in their marker. After a couple years of experimenting, and observing, I have found that suction timing usually occurs when the firing, and 3 way actuation are almost right on top of each other. The theory behind this is, that while the air is moving down the barrel from the shot, the breach is on its way open. The air moving down the barrel creates a vacuum in the breach, which sucks air from the hopper into it. It is still open for debate if this actually has any benefits, but it is still good for bragging rights. p of each other. The theory behind this is, that while the air is moving down the barrel from the shot, the breach is on its way open. The air moving down the barrel creates a vacuum in the breach, which sucks air from the hopper into it. It is still open for debate if this actually has any benefits, but it is still good for bragging rights.

http://www.endlesspb...ech/timing.html

Edited by Snipez4664, 20 November 2008 - 01:09 PM.

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#2 moyster14

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Posted 20 November 2008 - 01:24 PM

It makes a certain amount of sense I guess. If the poppet is closed or dump chamber is closed or empty, and the ball is still moving through the barrel, there would be a bit of a vacuum produced in the breech. But you would almost think the porting in the barrel would remedy it.

I think the vacuum timing of an autococker is a different beast. More of a aspirating type of effect.
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#3 oerllikon

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Posted 20 November 2008 - 03:45 PM

Yeah, this is pretty tricky. Is there a point between blowback, and vacuum timing? I want to try and get this to work, when i grab some air
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#4 Merc4Hire

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Posted 20 November 2008 - 07:49 PM

I realize that this forum discourages posting talk without data, but in autocockers, the theory behind vacuum timing isn't that the ball is pulling air behind it. Vacuum timing is based on having such a small bolt dwell that air is still traveling down the barrel when the breach begins to open causing a siphon effect. If your timing is just a hair more advanced, then you get substantial blowback.

Suction timing is actually pretty easy to achieve, and it is clearly demonstrable. I can suction time an autococker, put a paintball in the breach and the next shot will suck in a piece of toilet paper all the way into the breach. You can do it without a paintball in the breach, too, which shows that it isn't the paintball pulling air behind it, it is the siphon effect.

(If you time it for suction without paint in the breach you are likely to have intermittant blowback with paint. That is why it is easiest to adjust timing without paint using tp until you achieve suction and dial it back a notch as your starting point with paint. Of course all of this is a matter of preference, some people hate autocockers set up like this and want neither suction nor blowback.)

I would make a video to demonstrate this as 'data' but I only have a cell phone camera, so it would suck.


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#5 ABOMBER760

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Posted 20 November 2008 - 07:56 PM

^^why dont you borrow a camera?^^ I would love to see this done and a tutorial on it would flipping sweet.

#6 cockerpunk

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Posted 20 November 2008 - 08:08 PM

its fairly easy to do with a electro cocker. i know somehwer ethe is a video of the osiris cocker shooting like 10 BPS from a gravity feed loader because of suction timing.
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#7 chewiestmonkey

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Posted 20 November 2008 - 09:48 PM

its awsome when you have a suctioned timed cocker, cuz then you can say "my gun sucks balls" and mean it
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#8 brycelarson

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Posted 20 November 2008 - 10:13 PM

yeah, mine pulls TP into the breech - I figgure, why not gain mechanical advantage if possible.

As to whether it works with other guns - I don't know. Is it only a closed bolt thing?

I suppose the real question in the PunkWorks world is this:

Can a firing system reliably be tuned to pull the next ball into the breech?

As a second part of the question (since it seems that a cocker can do it)

Is this repeatable amongst different designs - or is it only in poppet, closed bolt markers?

And thirdly - is there a way to include this as part of a reliable loading assistance system in other marker designs?

Edited by brycelarson, 20 November 2008 - 10:13 PM.


#9 Lord Odin

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Posted 20 November 2008 - 10:15 PM

I would very much like to see a video of this. I've never heard of it before.

#10 brycelarson

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Posted 20 November 2008 - 10:24 PM

I would very much like to see a video of this. I've never heard of it before.


I'm closing on a house on Wednesday - I'll try to dig some gear out and do a vid when I can - but I don't know when I'll get to it.

The way I got mine to do it was to put a little ball of toilet paper in the feed neck ( I shoot a right feed cocker) as I timed it. There are three ways that the paper is going to go depending on how you set your three way activation to sear release:

1. the bolt opens before the air blast from the valve is complete - this is the closest you can get the timing and still have it working - the paper will blow out of the neck.

2. you can have the firing cycle complete before the three way activates the ram - this means the paper sits in place. This is the standard timing and is the most reliable for avoiding short stroking and doing weird stuff with the paint.

3. You can get the three way to open the bolt really close to the firing - and the paper will suck into the breech.

The third one is based on gun timing but also shooting rhythm. you have to pull the trigger pretty fast - the idea is that the ball is still movign down the barrel when the bolt opens - so there's still some suction. I don't know if that's what actually causes it - I would think that the ball leaves too quickly - but I have certainly seen and timed guns that will suction a light paper ball into the breech.

#11 cockerpunk

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Posted 20 November 2008 - 11:26 PM

i think it has more to do with the mass of the air. to have the bolt kick back during the time at which the ball is still in the barrel is way to fast.

meaning, the air actually has mass, and thus momentum. since it is being accelerated down the barrel, it has momentum in that direction.

so when the bolt opens up, the velocity of the air and its momentum is still for a small time moving and forcing forward.
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And yes, Gordon is the sexiest manifestation of "to the front."


#12 Lucas

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Posted 20 November 2008 - 11:27 PM

These threads are always so very interesting. Even thou I can't put much input into them because everything is basiclaly straightforward and said. But I find these threads very interesting because they reflect things such as Mechanics, air chambers, ct ect.

#13 Snipez4664

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Posted 21 November 2008 - 01:22 PM

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I was all ready to crunch the numbers and such, but then I realized we can just read the result off a transducer, and in fact, already have... Denying me this exercise in mental masturbation. :(
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#14 brycelarson

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Posted 21 November 2008 - 01:34 PM

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I was all ready to crunch the numbers and such, but then I realized we can just read the result off a transducer, and in fact, already have... Denying me this exercise in mental masturbation. :(


snipe - when has any form of masturbation been a necessity? Do it if you want, I certainly won't deny you. :D

#15 Snipez4664

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Posted 16 December 2008 - 11:18 AM

Today's happy thought - this is exactly analogous to exhaust scavenging.
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#16 Ando

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Posted 16 December 2008 - 02:15 PM

would one of those clear elbows for Spyders help with this to help view it better? Just a thought

#17 Merc4Hire

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Posted 26 December 2008 - 04:14 PM

I would very much like to see a video of this. I've never heard of it before.


I'm closing on a house on Wednesday - I'll try to dig some gear out and do a vid when I can - but I don't know when I'll get to it.

The way I got mine to do it was to put a little ball of toilet paper in the feed neck ( I shoot a right feed cocker) as I timed it. There are three ways that the paper is going to go depending on how you set your three way activation to sear release:

1. the bolt opens before the air blast from the valve is complete - this is the closest you can get the timing and still have it working - the paper will blow out of the neck.

2. you can have the firing cycle complete before the three way activates the ram - this means the paper sits in place. This is the standard timing and is the most reliable for avoiding short stroking and doing weird stuff with the paint.

3. You can get the three way to open the bolt really close to the firing - and the paper will suck into the breech.

The third one is based on gun timing but also shooting rhythm. you have to pull the trigger pretty fast - the idea is that the ball is still movign down the barrel when the bolt opens - so there's still some suction. I don't know if that's what actually causes it - I would think that the ball leaves too quickly - but I have certainly seen and timed guns that will suction a light paper ball into the breech.



My guns for my personal use are set up for style # 3 this is a trigger preference thing. it enables the gun to have a very short light trigger pull that is easy to be very quick with. you also have to be more consistent in the pull to avoid stroking issues. that isn't a problem for me though. I usually hand new people a cocker timed like this. If they have problems I hand them a gun timed #2 which I hate the feel of that. I explain how to fully pull and release the trigger to the #2 people and have pretty much no problems. If you set your suction in #3 style to the max suction, changes in paint diameter or feed issues can easily make it intermittantly a #1 which is bad. I dial it back a hair from this and have steady reliable suction. I also think the blowgun test variation effect is relevant to that phenomeonon because a significant change in back pressure in the barrel from paint match will affect the siphon effect.

Like bryce said it is nice to gain the extra mechanical avantage too, because you can. I have an e1 orracle with the old board set for suction and with a plain old revvy it is pretty light and I can shoot around 10+ bps with the eye off with little fear of getting a pinch or break, which is nice in weather that causes my eyes to fog. Or I can throw my cheetah halo on there... whatever.


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