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]

Barrel suck

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.