Barrel Suction

[AGD]

This is a good topic to start a new thread on.

In the past people have made the claim for setting up guns so they open the bolt in perfect time to "suck" the ball waiting into the breach. This has been demostrated by using a piece of tissue paper which disapears into the barrel after firing.

We have not actually done any research on this but we do have some data. My comments are in the "reasonably thought out logic" catagory.

In theory it is possible to create a vacume by getting air to all flow out the end of a tube. There are vacume generators that use compressed air to create vacume with no moving parts. Barrels do in fact get a vacume effect when fired and we have seen this when putting our pressure sensors in the barrel. We have actually detected a yo-yo effect where there is vacume in the barrel and the bolt opens. Air rushes in from both ends and builds up pressure then moves back out and in and out. Like a wave bouncing off two sides of a pool and meeting back up in the middle.

My strategic thinking tells me this, the whole pressure/depressure takes place in 5 thousands of a second with any vacume effect lasting for only a few milliseconds. Whatever physical effect the vacume is going to have has to happen QUICK! The super low mass of a piece of tissue allows it to react and get sucked into the barrel but the 1000x mass of the paintball has no hope of moving.

If I am wrong you should be able to hold a gun upside down with your finger holding the ball waiting in place. Fire the gun and see if the ball jumps off your finger. Or alternatively put the gun on its side and see if the ball rolls into the breach and how fast. If it just rolls in then it's not doing much to help you shoot fast.

My off handed opinion is the whole barrel sucking thing is just another myth and conjecture that drives the paintball religion.

AGD

[rjvemt1]

it seems that the seal around the incomming pb needed to maintain the intergity of the vacuum would counteract the minut vacuum in the first place.

[zvanut]

you know what Tom,

i know you are a very smart man, but i think i will try this myself and see what happens. (if i can get my hands on a few guns)

ill get pictures and maybe a video or two and let you know what happens.

[Wat]

Well, if there's someone with free time at agd...

You could suspend ball via a wire in the feedneck right above the bolt on a cocker. Attach the wire to a strain gauge of some sort, fire and measure any downward sucking forces on the ball.

My view on most of the paintball "technical talk" is that most people while directionally correct in their analysis, fail to comprehend the magnitude of effects. The increase in feed rate is probably a million times shorter in time than the amount of time the bolt is open. The pursuit for immeasurable and trivial performance gains in this sport is astounding. I'm just amazed at the hours and money spent for that 0.0001% performance gain when a few hours a week in the gym would greatly improve not only athletic aspect of the game, but also increase life expectancy and sexual attractiveness.

But call me a freak. I run a 5 year old stock minimag as my primary gun now.

[rjvemt1]

few hours a week in the gym would greatly improve not only athletic aspect of the game yup and maybe not finish the 12 pack friday night.

[ts1spoc]

Sound like a venturi effect where a large stream of air or fluid is blow over a smaller orfice at a right angle and the high volume flow creates a negative pressure on the smaller opening thereby drawing any material inside the small orfice into the large stream. The yoyo effect also sounds like water hammer. In an older home if you turn on a faucet all the way then suddenly shut it off the pipes rattle. The water has been traveling forward and suddenly stops. Since water is non-compressible it rebounds off the closed valve all the way back up the line. In some cases it will cause a pipe to burst. If you watch firemen when they shut down a hose they close the water valve slowly. Closing it quickly will shell the pump and rupture a water main. With air, since it's compressible, it would not be as damaging.
My guess is that with a recessed bolt face the Bernoulli Principal would draw the ball into the bolt cup as the bolt started forward and the air began to flow around the ball then cause it to impact the bolt. Just from watching my gun as it cycles the amount of blow by around the bolt is greater than any vacuum created by the air rushing across the ball opening afterwards.
Just for discussion purposes I would say that sucking the ball into the chamber is a myth.

[Vegeta]

Did I inspire this thread? neat-o.....

Tom, you stated this vacuum effect happens in 5 thousands of a second. Now unless the bolt opens far enough to give a gap for the ball to be sucked down in 5 thousandths of a second, all this will do is pull a bit of pull on the ball, but if the gap in the breech and bolt isnt big enough in 5 thousandths of a second to allow for a ball to pass down into the breech, this would not suck the ball into the chamber, for you cant pull a .68 calibre paintball through a gap in the bolt/gun thats less than that. And if the vacuum is gone in .005 seconds, and hte bolt is not open far enough in that time, well the ball can't be sucked in now can it.

Tom if you have the data of how long it takes the bolt to open, it would help.

Another question is, could this effect be measured on a mag? I belive we are talking mainly about cockers here, since hte bolt it totally sealed in the barrel before the gas is let out.

[nicad]

..as far as amount of time a cocker takes to perform its duties, it is VERY helpful to turn to the RaceFrame. ofcourse every cocker is setup different, but we see that most can open the bolt (remember its dragging the hammer back and compressing the main spring) in about 30ms, some in the 20ms if your good. :)

Vegeta- that would mean your correct in saying the bolt isnt fully open in 5ms, which according to Tom is how long he says the suction lasts.

however, i personally believe in ball suction. this is all based on my un-official observances, and I think it has more to do with a continuation of air flow OUT the barrel, instead of the yo-yo as Tom was speaking about. Tom- these tests that yall saw this occuring, was it on an autococker or an automag?

I do what reality tells me. :)

[Vegeta]

Well, I'm definately not seeing anything of the such on my mag, but of course this is mainly cockers were talking here, but on the off hand, I'm seeing balls in the feed stack jump a ball's lenghh if s large stack isnt on top of them.

[xatle]

ok, heres my problem...
if the round being fired is still in the barrel then doesnt any air flow in the barrel translate into pressure? so in order for the feed tube to feel any suction the round fired would have to have left the barrel and the bolt would have to open while still dumping air flow, reducing the efficiancy per shot, otherwise the feed tube would act as an exit for the pressure inside the barrel, or am i just thinking badly?

nicad, when you say continuation of air flow out of the barrel, do you mean a mass of air traveling down the barrel pushing a ball in front of it and pulling the next ball in behind it or do you mean that the pressure in the barrel reaches ambient external pressure before the ball exits and the inertia of the ball creats suction in the barrel pulling the next ball through the well timed opening of the breach?

[Wat]

Fluids is hard guys. You really really need to have taken university courses in it and actually work in fluids. I took a year of fluid/thermo dynamics at MIT and i must say, it never really stuck in my head because unlike materials or mechanics or dynamics, its just not something one can easily picture going on. Its incredibly complicated and the one thing i've learned is that in the real world, thought analysis and pencil and paper calculations can't cut it. You have to run models, simulations and experiments to figure things out.

An experiment we can easily see is what tom points out, the sucking of tissue paper. And like tom said, there's a difference between sucking tissue and a paintball thats 1000x heaver.

[Kaiser Bob]

Also a tissue makes a full seal around the feed tube, where a paintball would not...

[AGD]

Well as expected this thread is generating lots of discussion. Someone should try the test and report back here. Heck I could be wrong or missing something. Like I said it's a reasonably thought out conclusion but might not reflect reality.

It takes about 14 ms for the average bolt to open. The balls bobble because they are getting hit by the bolt and the blowby.

AGD

[Dubstar112]

Im pretty sure that to get ball suck, you have to make your gun slightly tweaked for timing. This could mean the ball is firing later in the cycle, and that 5ms delay could be just enough for the trigger to be pulled again, creating a gap in the bolt and body. I dont belive this would work. It could, but the way I see it a paintball is heavier than the vacuum source.

What if you used a 16 inch unported barrel on a closed bolt gun, with REALLY good paintmatch.... Take one shot with out opening the bolt after that shot. That should make the ball go really slow.

[zvanut]

alright guys,

after doing a bit of redearch on my own (and with the help of scorch) i have learned these things

greater flow = easier to create suction

oring elimnate blowback

timing = key factor

scorch also stated that the Mac Dev Sonic Cockers and Vital Ultra Sonic Cockers get "Extreme" suction.

i will hopefully be sending the money out for my cocker on monday (YAY :)) and will conduct a few tests and report back.

::edit~~ another thing is the cocker im getting is right feed. im thinking that this MAY actually have an effect on the bolt suction. how it will have an effect i am not sure yet, but i will "sleep on it" :) and report back later.

[Mossman]

Originally posted by Vegeta
Did I inspire this thread? neat-o.....

Tom, you stated this vacuum effect happens in 5 thousands of a second. Now unless the bolt opens far enough to give a gap for the ball to be sucked down in 5 thousandths of a second, all this will do is pull a bit of pull on the ball, but if the gap in the breech and bolt isnt big enough in 5 thousandths of a second to allow for a ball to pass down into the breech, this would not suck the ball into the chamber, for you cant pull a .68 calibre paintball through a gap in the bolt/gun thats less than that. And if the vacuum is gone in .005 seconds, and hte bolt is not open far enough in that time, well the ball can't be sucked in now can it.

Tom if you have the data of how long it takes the bolt to open, it would help.


This is very true. The fact of the matter is, If there is no seal made, (like a mag), and I dont think cockers are completely sealed, There is a very tiny chance that there is absolutely no blow or suck on the ball. I dont see how that could be an equilibrium, there will always be one or the other.

If there is suck, and it only lasts. .005 seconds, and the bolt isnt open the size of a paintball by then, true, chances are it does nothing for the speed of the ball to fall into the breach. On the other hand, I could see a light "puff" of air out of the edge of the bolt that does open in those .005 seconds doing some damage. That is what the mag is aparently victim to, although Ive never used my SF body, and never used a VF, so I dont really know first hand.

Anyhow, while a myth or whatever it is, if the chamber isnt sealed while the bolt is moving, and if there is air or lack of air in the chamber at this time, it CANT be worse to have suck than blow as far as I see it.

[RT_Luver]

to many big words...the only one I really knew was vacume(and yes, i dont mean the thing you use to clean floors, though thats probably where the vacume cleaner got its name)

[liigod]

yes a tissue is very light. On my timmy the tissue doesnt move at all, which means the balls fall freely. On my f5 the tissue is sucked well into the barrel, which means that a ball can only be helped, not hurt by this. Either way, i just dont like it how with my old mag i could load 4 balls into the vert feed, and 3 would jump out when i fired.

[pbjosh]

Sorry for not posting sooner, I have been 1 busy man!

Okay, I also thought 'Ball Suck' was a total myth.

Then I got the Racegun grip for the 'Cocker and started playing around.

A couple of things. Cockers need to have a good sealing bolt, no matter what. If they don't ball suck won't happen. In fact, with alot of the o-ringless bolt tips I have found I can't even feed them with a HALO. A 'SuperFly' bolt has about a .68 od, while the Breech is about .689 or so.

As for 'Ball Suck' I found it while playing and testing Blowback and Dell settings. Since I can adjust the dwell by the millisecond (.001 of a second) and the open times I can tune in the cycle of the 'Cockers to have the bolt open right after the hammer drops.

I had a gun set to 5 ms for the dwell. I noticed I had some blowback. Just a hint. This was on a gun that had a long valve dwell. I was testing with tissue. After I added 3ms I noticed serious 'Ball Suck' on the tissue. Then I did the tissue test with paint. I had to add 1 ms to get ball suck again, and then after that, the gun fed like a charm.

After testing and setting the gun to 6-9 ms (depending on the gun) I can normally run at a really high ROF using a non-motorized hopper (VL200) and feed reliably with the gun turned 75-80 degrees to either side, with a halfway full loader. With the Eye installed, I have notice NO significant ROF changes between the motorized hoppers and the VL200.

So, can 'Ball Suck' be tuned in? Yup, but if it is off by a millisec or 2 it will not be noticed. Also you have to time with paint in there, and your bolt must have NO blowback to be able to even find it. With almost no bolt being made for the 'Cocker these days with a front o-ring, and some of the delrin bolts being far to small to seal, you will have a much harder time testing 'Ball Suck' than you realize.

And like AGD asked, is it really noticed? A bit. But for all the hype, 'Ball Suck' is not that big of a deal, just a neat trick, that can help the way you feed, but not to much.

Josh

[Bunkrking]

Expierienced cocker owners know you should never time a cocker without shooting paint through it. If you time a cocker too close without shooting paint through the barrel and then you go to play you will get severe blowback. You want the ball to get to the porting part of the barrel before the bolt opens up the breech for another paintball to drop. If the timing is too close as I stated before the air pressure behind the ball has no place to go but up the feed neck. If the ball leaves the breech going 300 fps an your porting doesn't start untill 6" up the barrel you need to give the ball 1/600 of a second to reach the porting. If the portin start further back than your gun can be timed closer. Don't think of a cocker having suction to suck balls into the feed tube for a faster feed rate, but a result of zero blowback.

[nicad]

pbjosh-
i put an oring in an older (shocktech?) bolt tip.. so that it now has 3 orings.. helped feeding tremendously! This particular setup had been getting some extreme blow by past the bolt tip..
there is a slight problem with it now though, and this may be why not many (or any) bolts have a third oring in the tip. when firing paint out, as the bolt opens in the nomal cycle, the oring will flare out a bit and catch on the lip of the breech's feed hole, and sometimes preventing the bolt from moving back all the way. might just be a sharp edge on the feed hole/breech, but it does it on two different bodies here.. :-/

out!

[BenD]

hey,

dont know if this pertains.... but check this video out, it shows tissue getting sucked in...

http://home.attbi.com/~blindseaman/index4.html

isnt working for me, but mabye it will for you

[athomas]

Ball suck. Hmmmm.

Here's how to achieve it. Fire a ball down a barrel and maintain a closed bolt until the ball has exited the barrel ( ~5ms from the time the gas starts to flow. Actual time may be slightly longer from initial trigger pull, ie. dwell setting). Open/retract the bolt. Two things happen. First, the momentum of the air traveling out the end of the barrel creates a slight vacuum effect in the barrel. Second, the bolt retracting to open creates additional space for air to occupy. Combine the two and you get the vacuum effect. How much of an effect depends on the momentum of the air moving out the barrel and the return speed of the bolt.

[Vegeta]

OK.. so you want to keep the bolt closed until right as hte ball comes out of hte barrel, therefore having hte ball pull out and the bolt pull on hte air, creating a nice vaccum.. well unless you can fling that bolt open in a few miliseconds, you have no chance of sucking a ball down the breech. Once that bolt is cracked open, you only have a few miliseconds before hte vaccum is gone. If hte bolt isn't opened wide enough to let a ball drop by the time the vacuum is gone, it won't suck the ball at all. The entire idea is hard to come by unless you, like Josh stated, have a race frame and time the components separately to their needs.

[Webmaster]

In my experience - "suction" does happen on cockers if they are timed right. I can get toilet paper OUT of the barrel with one shot. (sitting on the side of the feed tube, it is shot out of the barrel when shot).

In my expericance - it is a pretty fine line. You may get the first shot to "suck" - but if you do rapid fire you actually get SOME blow back - as the line is very fine and the sloppiness of the mechanics allow the guns fire point to change slightly due to the way the trigger is pulled etc.

In my expericance, it really doesnt have any EFFECT on the paintball. As you pointed out - the time and forces involved are too minute to effect the larger sized paintball.

Since I can still chop in my cocker some times (esp if I dont turn on the revvy) I do not believe that this event does anything POSITIVE - but it is a good indicator that your gun is properly timed.

Now as to WHY this happens - Im not that smart. I know it has NOTHING to do with the ball - infact perhaps this event goes away with paint in the gun. When the test is done, its a piece of tissue on the bolt or feed tube, the gun is fired and even with the bolt in the open position the tissue is sucked out.

[athomas]

Originally posted by Webmaster
In my experience - "suction" does happen on cockers if they are timed right. I can get toilet paper OUT of the barrel with one shot. (sitting on the side of the feed tube, it is shot out of the barrel when shot).

In my expericance - it is a pretty fine line. You may get the first shot to "suck" - but if you do rapid fire you actually get SOME blow back - as the line is very fine and the sloppiness of the mechanics allow the guns fire point to change slightly due to the way the trigger is pulled etc.


When dry firing, you only have to get the air moving to experience the effect. Its harder to do when firing a ball. You have to set the dwell long enough to allow the ball to exit or be near the exit of the barrel before you start to pull the bolt back. Then, as Vegeta has stated, you have to pull the bolt back fast enough to allow the vacuum to be present while the bolt is fully open. A tissue is not so critical as it will get pulled into the breach before the bolt is fully retracted.

Interesting effect though.

If I were timing a cocker, I'd set the dwell to give as close to zero vacuum as possible. That would mean there is the least amount of pressure differential in and around the barrel and the best air efficiency.

[tomass15]

The Idea of barrell suck is not bad, it's just not going to happen with paintball guns as we know them. The sucking of the ball is supposed to be coming from the low pressure created by the bolt moving. The bolt movement thus makes a low pressure by enlarging the area the same amount of air has to fill. The problem is the big old hole at the end of the barrel and the many little ones on most barrels we now use. If you could have a check valve type mechanisim on your non ported barrel, you may be able to get enough low pressure built up to suck in a paint ball, but due to the path of least resistance the low pressure will be filled by air from the end of the barrel and ports. This creates the wave motion Tom talked about. Porting also helps settle down these waves.

Add a new angle, if there was that much suction created, if the bolt began to move backwards before the ball left the barrel, the ball would be slowed by the change from positive to negative pressure...

Lastly, it wouldn't matter if the design was open or closed bolt, it still acts as a poor sealed piston. If there was suction, then why do the guns feed better with a design like power feed?

[Bunkrking]

intereting theory tomass, but when you time a cocker too close so that the breech opens up too early then you get blowback from the air coming out of the bolt when the bolt starts too clear the breech. If the air vents out of the gun before the bolt opens then you get no blowback. If the bolt clears the breech right as the panitball is leaving the barrel then you will get a larger space with the same amount of air from the tip of the barrel to the breech (ofcoarse only if you use a non-ported barrel) then you get a suction.

[314159]

i think the ball leaves the barrel long before the back block starts to open.

my reasoning behind this is my pgp, the bolt is just sitting there (has the berrings removed). when i fire the pgp without holding the pump arm and bolt forward, the bolt pops back, and there is a good amount of gas vented out of the top of the feed port, but over a chronograph it only drops 10 fps or so compared to when i would hold the pump arm forward. this means, as far as the ball sticking around in the barrel, whatever it does, it is gone fast.

and the ball is gone while the barrel is still mostly preasurised in the pgp's case.




i think that in order to increase feed speed x amount, how much suction would be needed would be a good way to think about it.

[Pstan]

You could use the "Big Man's" basic test as a way to see the suction if it does truly occur. Invert a verticle feed cocker in a gun vise. Then place a paintball on a drinking straw much like a Golf ball sits on a tee. By doing this, you take a great deal of human error out of the equation. Lower the inverted gun onto the paintball situated on it's "tee" to the point that it is in the same position it would be in a non-inverted gun. Fire the gun and see if the ball jumps off it's "tee".

And for those that wouldnt mind ruining their gun to prove a point. Just seal off any holes designed at reducing blowback and lower the gun so that the feed is submerged in a drinking glass of water. Fire. If suction occurs, water should be drawn up the barrel. Or, you should at least see the water level rise.... then fall. I suppose blowback would bubble the water and suction would draw it in.......presuming you seal things off before you start.


Better yet........seal the feed neck with the straw in place and lower the straw into the water. Blowback will create bubbles.......suction will draw water up the tube of the straw.

Just a couple of random thoughts......


Pstan

[the electrician]

it seems to me that pulling the ball upward against gravity would show that there is suction, but I don't see it happening.actually in real loading conditions, the suction would be aiding gravity in its job of pulling the ball down into the chamber. so instead of doing a 180 and making it go against gravity, put the gun on it's side, in a clamp, and put a level on it. level it out and set a ballin the feed tube, next to the closed bolt.
my guess is that if there is some suction that it isn't enough to help the loading process. the feed port would have to be smaller, closer to the size of the paintball it seems.