The inner diameter of barrels...

[echoes]

I'm not quite sure if this belongs in this forum, but I was just looking at www.durtydan.com and here's what he had to say about barrel ID:

"BARREL INNER DIAMETER

I have read several articles on how to match your paint to your barrel, and vice versa. The authors claim that you must match your barrel inner diameter with that of the paintball's outer diameter.

I'm here to tell you that this is a big load of crap. So long as the paint doesn't roll out the barrel before you fire it and it feeds properly, your barrel inner diameter has nothing to do with the ballistic performance of the paintball.

Some will say that if you put big bore paint in a small bore barrel, the ball will slow down. SO? Adjust your marker's velocity accordingly. Any more questions?

You see, when you fire the ball, it gets compressed and if fits the barrel perfectly. Some airsmiths and barrel manufacturers "step tune" their barrels. Tight at the bore (to stop roll out), wider in the middle (to allow for ball expansion) and tight at the end (for accuracy). I've used step-tuned barrels with varying degrees of success ranging from "absolutely amazing" to "it'll do fine".

What IS important is barrel LENGTH. Any airsmith will tell you that. That is, any airsmith that doesn't make his money by making and selling barrels of different diameters. Here's the scoop.

If you are using CO2 the gas will expand more efficiently the warmer the air temperature is. Therefore you should use a shorter barrel when it's hot and a longer barrel when it's cold. Nothing shorter than nine inches and nothing longer than 12 inches (unless they're vented and you can get away with adding an inch).

With high pressure air, you can have any length (9-12 inches, unvented) because the air temperature doesn't effect the high pressure system as much.

Anybody who tell you otherwise doesn't know what they're talking about. Or they do and they want you to buy their barrels."

While what he says in the third paragraph may be true, it will hurt efficiency. I'm not quite sure what I think of this though.

Elsewhere he mentioned how it doesn't make sense to obsess over matching paint to your barrel because paint isn't perfectly round, making it futile to worry about whether or not your .688 barrel is a better match than your .689 barrel. That I do agree with. For me at least, it isn't worthwhile owning a Freak and having 8 different bore sizes to choose from. But maybe that's just because I almost always shoot the same size paint.

The full article can be read here.

[athomas]

Some of the article is true to a point. Tiny differences in paint to barrel match aren't much of an issue. Most of the time the paint itself has large margins of error. As for adjusting the velocity to compensate for the "wrong size paint", this works to an extent but the main reason we size the barrel is for consistency. Any time you introduce an increase in friction as a variable in the operation of the marker you will have variable results.

An excessively tight bore will cause some paint to shoot without much variance while another shot might bind a bit causing a lower velocity. A tight bore is also harder on brittle paint because you have to increase the force with which the bolt pushes the ball into the barrel.

On the other side of the coin, a loose barrel causes ball wobble as it is being shot. It is effectively the same as a speed wobble and results in an icrease in friction which slows down the velocity of the ball. The next shot might go perfectly guided, while a third might ride on one side of the barrel causing the ball to develope a spin.

A sized barrel allows us to start at an "ideal" starting point. Now if larger or smaller paint is introduced due to manufacturing inconsistencies, they won't have much of an impact on the performance of the gun.

The length issue varies from gun to gun due to the distance required to accelerate the ball to the desired velocity at that gun's operating pressure. Porting has a big affect on this.

There are no hard and fast "this is the way it is" facts. Barrels for the most part are very forgiving on most paint. Two or three "good" barrels of various sizes are probably adequate for most guns to shoot most balls. The smoother the bore, the more forgiving the barrel will be.

[FatMan]

I have definitely experienced inconsistency when the bore was too big, and I've experienced breakage when the bore was too small. I would tend to think efficiency is also affected.

I must admit that my experience with inconsistency was from a time when I shot a closed-bolt marker. I can't say for sure that the mag has the same result.

I would tend to think that in any marker too loose a bore would result in uneven friction on the ball, possibly a small amount of spin or instability.

I don't know much about deformation of the ball. The end result may be that the range of sizes of your bore doesn't need to be so fine - so maybe two or three sizes is all you need.

I would certainly like to see this issue put to the test scientifically.

FatMan

[echoes]

Originally posted by FatMan
I would certainly like to see this issue put to the test scientifically.

Yeah, it's this claim that interests me the most: "You see, when you fire the ball, it gets compressed and if fits the barrel perfectly."

[FatMan]

Originally posted by Arno


Yeah, it's this claim that interests me the most: "You see, when you fire the ball, it gets compressed and if fits the barrel perfectly."

Yeah - so I'm thinking - if the ball fits very loose in the barrel, why does it compress, when it could get get moving on down the barrel? Now, if there was resistance to moving, because, oh, I don't know, the ball fits tight, THEN I could imagine it getting compressed and deformed.

My gut tells me that if the barrel is loose enough that the ball falls through, then no compression/deformation is going to make much of a difference. On the other hand, the barrel being too tight can certainly be a problem - especially with brittle paint.

I mean, the proper way to size your barrel (if you do that, like I do with a Freak) you select the largest bore where the paint doesn't fall through (and you test several balls to make sure you didn't get the largest one).

I think for many players, a single large-bore barrel is fine, and a small bore is nice if you play with various brands of paint. Serious players who want serious consistency want somethink like a Freak.

But I'd STILL like to see that confirmed in the lab.

FatMan

[FatMan]

Any comments Paladin?

It seems to me Paladin has had some experience with this stuff - I remember reading somewhere about "eliptically honed" barrels and stuff. I don't know if he's reading this thread, but I'd like to hear his comments if he is.

FatMan

[hitech]

I challenge anyone to find a properly controlled test that shows a "properly" matched barrel is any more accurate.

[athomas]

Its easy to see the extremes of an experiment of large and small bores on paintball. Use a barrel of about .687 - .688 and Diablo blaze. They match up pretty well. Now use a bore of around .695 and then .682 and see how it shoots. Use a freak type interchangeable bore system. That way all other factors such as barrel style are the same.

The balls will fire but you will notice inconsistency and inaccuracy on the bores which are too tight and too loose.

These are magnified examples of what improperly sized barrels will do for a paintball, but they serve to illustrate the effects.

[hitech]

Originally posted by athomas
Its easy to see the extremes of an experiment of large and small bores on paintball. Use a barrel of about .687 - .688 and Diablo blaze. They match up pretty well. Now use a bore of around .695 and then .682 and see how it shoots...

To do a properly controlled test you have to do more than see how well it shoots. The marker must be "bench mounted". ALL other variables must be the same except the paint to barrel match, including velocity.

[echoes]

I fail to see why different bore sizes would affect accuracy. Whether or not the barrel is too small, too big, or just right, it has the same constant effect, meaning that Blaze in a .682 may be a tight fit, but it will be a tight fit all the way around the ball, so any detrimental effects on accuracy would be negated by the fact that it affects the ball equally, everywhere that the ball touches the barrel. The same should apply for a large or medium barrel.

[FooTemps]

The bore of the barrel effects efficiency more than anything but it will affect consistency, accuracy and breaks too.

Tight bore barrels matched with brittle large bore paint will obviously break in almost every case during the acceleration from 0-300 feet per second. A hard, paper thin, gelatain shell has problems going through bores that don't fit perfectly if it isn't matched well. The friction brings down the efficiency because you need more power to get the ball to the speed in that 9-12 inches. The more power needed the more gas wasted.
For accuracy and consistency, the paint is never always perfect. The diviance in bore sizes will always change the velocity. If you pick up a pack of brass eagle paint or big ball and put it into a small bore cp barrel you'll get inconsistent velocity because the brass eagle paintballs aren't very consistent on bore sizes. The bigger the ball the more the friction. Since, the brass eagle paint has more variations in paint size you'd get inconsistent velocity in your shots. The accuracy is effected because the more friction the more of a chance for spin. Afer the ball comes out of the muzzle of the barrel the release of the air pressure might also throw the ball off course. The tighter the paint the more the air, that means there's more air pressure to mess up the accuracy.

[echoes]

Originally posted by FooTemps
Tight bore barrels matched with brittle large bore paint will obviously break in almost every case during the acceleration from 0-300 feet per second. A hard, paper thin, gelatain shell has problems going through bores that don't fit perfectly if it isn't matched well. The friction brings down the efficiency because you need more power to get the ball to the speed in that 9-12 inches. The more power needed the more gas wasted.
For accuracy and consistency, the paint is never always perfect. The diviance in bore sizes will always change the velocity. If you pick up a pack of brass eagle paint or big ball and put it into a small bore cp barrel you'll get inconsistent velocity because the brass eagle paintballs aren't very consistent on bore sizes. The bigger the ball the more the friction. Since, the brass eagle paint has more variations in paint size you'd get inconsistent velocity in your shots. The accuracy is effected because the more friction the more of a chance for spin. Afer the ball comes out of the muzzle of the barrel the release of the air pressure might also throw the ball off course. The tighter the paint the more the air, that means there's more air pressure to mess up the accuracy.

Well of course it will be less efficient and you may break more paint, but I don't see how the increased friction increases the chance of the ball spinning. The increased friction slows down the ball everywhere uniformly, so I don't see why one side should start moving faster and therefore causing it to spin.

[FooTemps]

Originally posted by Arno


Well of course it will be less efficient and you may break more paint, but I don't see how the increased friction increases the chance of the ball spinning. The increased friction slows down the ball everywhere uniformly, so I don't see why one side should start moving faster and therefore causing it to spin.

Reason why tighter is worse for accuracy: Not every barrel is honed perfectly... Also there maybe be some shell or maybe some dried flaky paint or dirt on one side of the barrel that wasn't completely clean out..

[echoes]

Originally posted by FooTemps
Reason why tighter is worse for accuracy: Not every barrel is honed perfectly... Also there maybe be some shell or maybe some dried flaky paint or dirt on one side of the barrel that wasn't completely clean out..

A barrel that matches the paint perfectly can also have imperfect honing. And again, broken paint can happen in any barrel...

Just to clarify, let's assume that all other variables besides the differences in barrel bore size are constant. If a tight barrel is evenly honed(which we assume it is for the purposes of this discussion), then why should it be any less accurate than the same barrel with a larger boresize which is also well-honed(think Lapco autospirit vs Bigshot)? Less efficient and more likely to break balls, certainly, but I don't see how it would be less accurate.

[athomas]

What I mentioned before was an exagerated test that you could actually see the results with your eyes without the need for a bench mounted test (and beleive me, you would see the results). For real testing a bench mounted gun would be required.

In an ideal world where the paintballs are perfectly round, a tight bore or a not so tight bore wouldn't cause the gun to shoot inaccurately. The fact is, that the paintballs in all cases (even the best ones) are not round. They have a seam where the two halves are joined. It's this seam that causes most of the headaches.

By matching the bore of the barrel to the size of the paint we are using the barrel as a guide. The ball only touches the barrel in two places (where the seam is). The friction at the two points is so small that any air force behind the ball pushes the ball out the barrel. There is no spin induced because the forces are equal around the ball where there is no contact.

In a barrel that is too big, the ball only makes contact at one spot at a time. The barrel still acts like a guide but the ball is allowed to roll along the edge that it contacts because that is the point of highest friction.

In a barrel that is too small, the frictional forces are inconsistent and dependent on how the ball sits in the barrel. It doesn't roll in the barrel but when it exits the end, the final positioning can determine whether the air blast escapes evenly around it. If it catches a seam, a spin can be induced.

The whole premise of venting in a barrel was first used only as a muzzle brake to evenly disperse the air around the ball as it exited the barrel. It was especially noticeable when using poor quality paint. You could take the brake off or put it on and see immediate results. Now this brake is integrated into the barrels to the point where most of the barrel is vented. Only the first 4 - 6 inches is actually a barrel, the rest is just a guide to disperse air and prevent spin. The theory is that the ball rides through the last section of the barrel surrounded by an even cushion of air.