Internal porting?

[paintposse]

the porting makes the gun very quite but lose air efficency but a barrrel with out any ports sounds like a shotgun. there is pressure behind the ball that pushes the ball forward. if there are no ports the ball would have a greater amout of pressure behind it longer. but at the end it would be loud becouse of the great amount of pressure relesases. with ports the air is gradually released creating less ad less pressure so the ball will slow down towards the end of the barrel but it will be quiet. With a parted barrel u would need to raise your volocity to balance the loss of pressure making ur gun suck up more gas. But a barrel without porting would sound like a mini pipe bomb. it has the same principle.

[athomas]

Using good paint and a good paint to barrel match, porting does not seem to have much affect other than reducing efficiency and providing a silencing effect. Most ported barrels that people use are step drilled. The barrel extension is actuall a larger bore than the breach area of the barrel. This extension is the part that is ported. It is the larger diameter in the barrel extension that is providing more stability to the ball than the porting that is drilled in it.

[314159]

Originally posted by athomas
It is the larger diameter in the barrel extension that is providing more stability to the ball than the porting that is drilled in it.

so a larger diamater tube for a paintball to shoot through is more accurate because it provides stability? that is like saying big bore barrels are more accurate because they provide more stability.

the 2nd stage of the barrel does not do much at all, (it adds a fraction of its lenght to the effective barrel length equilivant of an unported length of the barrel)

it can be hard to clean out a 2 stage barrel well on the field also.

[paintposse]

i tried it and it doesnt work. it makes the barrel pratically a barrel with no ports but with bad air efficency. What i didnt was that taped some cloth around my barrel and put a pvc pipe over that. It was practically somethin inbetween a ported and non ported barrel

[Mossman]

I couldn't imagine it could help anything

[athomas]

Originally posted by 314159


so a larger diamater tube for a paintball to shoot through is more accurate because it provides stability? that is like saying big bore barrels are more accurate because they provide more stability.

Not quite true. In the stepped barrels, the effective barrel length for propulsion is the first section that is tighter. This starts the ball on its way and must fit the ball to provide a stable flight. The larger stepped estension acts as a guide only to keep an already straight shot, straight.

If a barrel starts larger than the ball, the pressure can cause acceleration in many different directions that would cause wobble as the ball travelled down the barrel or can start a spin if the ball starts rolling down just one side of the barrel.

Once the ball gets moving in a straight line, it only needs a straight guide to hold it on its path. You actually want to remove any interference that would cause otherwise. Interference could be in the inconsistencies in the surface smoothness due to dirt or residue.

The extension bore size can't be too exaggerated either or it is useless. It must still provide function as an extension of the barrel to maintain acceleration on the ball.

[314159]

Originally posted by athomas
Not quite true. In the stepped barrels, the effective barrel length for propulsion is the first section that is tighter. This starts the ball on its way and must fit the ball to provide a stable flight. The larger stepped estension acts as a guide only to keep an already straight shot, straight.

effective length of a ported barrel, is the lenght of a non ported barrel, with the same inner diamiter, that will shoot at the same velocity. a 12 inch barrel, with 6 inches unported, and 6 inches ported would have a longer effective length than 6 inches. why? because the ball still accelerates a little bit in the ported section of the barrel.

and as far as what you are saying, if the ball is still acelerating, in a larger bore (2nd stage), how is this different from just shooting a ball in a large bore barrel?

[hitech]

Originally posted by 314159
...A 12 inch barrel, with 6 inches unported, and 6 inches ported would have a longer effective length than 6 inches. Why? Because the ball still accelerates a little bit in the ported section of the barrel...

Tom doesn't agree with you. Here is a quote from his tech tip:

It is simple to understand that the harder you push something the faster it will accelerate and get up to speed in a shorter distance. So what distance do we have to get the ball up to speed? The effective length of the barrel is from the balls position before it's fired, to the place in the barrel where the pressure gets released, This is usually at the first porting holes or the step in the barrel. Porting is there to release gas pressure!! You are effectively stopping the acceleration at the ports so your 14" barrel that is half full of holes only has an effective length of 7".

[SlartyBartFast]

Well Tom can be wrong you know.

I can here the cries from the villagers with the pitchforks now:
HERESY!! HERESY!! Out with the heathen!

The loss of pressure due to the porting isn't instantaneous so the ball will still experience some accelerating pressure. But Tom is probably mostly correct. WHen you look at it the majority of the acceleration of a ball happens in the first 3 inches anyways.

[314159]

hitech, then what would you call the aproximation of a ported barrels equilivant non ported barrel.

toms model is functional, but it is a first aproximation.

this model would be a second aproximation.

[athomas]

I have to agree with 314159 in that the ball will still accelerate some in the ported extension. How much depends on the porting which will dictate how much of the pressure is vented off and how quickly. You can check this by holding your hand over the end of a ported barrel and blowing into the breach end. You don't get much resistance. Now, start covering the holes along the barrel. As you cover more of the holes , you will start to notice more resistance. That means there is pressure available behind the ball to provide acceleration.


Back to my explaination of large bore extensions:

A ball reaches most of its velocity in the first 3 - 4 inches of barrel length. The remainder of the barrel just completes the acceleration to maximum velocity. In the first few inches, its also hard to impart a spin on the ball. Once the ball is in motion in a straight trajectory without spin or wobble, its path can't be easily altered unless it comes in contact with something. The larger bore extension can still provide a guide for the ball where the ball travels pushed by a cushion of air. The ball contact with the inside of the barrel is minimal so not much affect by contact to alter the trajectory. If a ball starts a spin in the first few inches it can't be maintained once the extension is reached because much of the force around the ball is equalized.

A barrel with the same bore throughout its length, works well if all factors are good. If any other factor starts a deflection, it may cause the ball to start spinning and will be maintained throught the remainder of the barrel. This just means that the rate of spin will accelerate as it travels down the barrel in contact with the sides of the barrel.

[hitech]

Originally posted by 314159
hitech, then what would you call the approximation of a ported barrels equivalent non ported barrel?

Are you asking what the effective length of a ported barrel is? I'm not sure what you mean by "the approximation of a ... equivalent". All other factors equal, a ported barrel will fire a paintball with slightly less velocity than a non ported barrel that is the same length as the non ported length of the ported barrel. At least that is what Tom is saying, and he is the only one I know who has tested his theories and "published" them. I'm buying it until someone can show him to be wrong.

[314159]

tom is saying that the effective lenght of a barrel is where the porting stops. i say that this is a first aproximation, because the ball still accelerates in the ported section.

a second aproximation, takes the ported section into effect, and would give you a lenght of an unported barrel, that would have the same velocity, and characteristics of the longer, ported barrel. this number is more usefull for calculations, but is also harder to get.

bolth of these numbers are the effective length of the barrel, it is just for most uses, the first aproximation is fine. i am shure that tom realises that, and so he will use that form when it suits the topic.



the point that i am trying to make, is that i am trying to make, is that i do not feel that ported barrels are more accurate than non ported barrels.

as far as 2 stage barrels, because the ball still accelerates in the second stage, it has a chance to be affected by the air accelerating it. because it has a larger bore, it would have the chance to bounce around (further testing is needed) or it could just fly straight. i think that if i wanted to stabolise a paintball, i would raither just have a barrel that would not let the ball wobble.

[confedman75]

the frames per second wasnt working quite right on my comp so i did 2 one realy fast and one realy slow(flash, gif)
its an anitmation that i whipped up showing how an internally ported barrel would remove vaccuum.

http://pro-mktg.com/MAIN/images/Untitled-1.htm

[athomas]

confedman75

At the end of the barrel when a ball exits, there isn't much excess air pressure behind the ball. The energy contained by the moving ball would be so much greater than the force of the air moving around it, that there would be no noticable deflection in the ball.

The point is you can't get enough air behind it to fill any vaccuum void if it did exist. If you did,it would be a waste of air and you would get terrible efficiency.