The inner diameter of barrels...

[athomas]

I remember my first encounter with paint of various sizes. Back in 1990, I had just purchased a second barrel with a larger bore for my pump gun, not because I wanted to be able to shoot different sized paintball, but because they were classed for winter or summer play. The small barrel .6875 was winter and .6925 was summer. Both barrels were like mirrors inside so quality of honing was not an issue.

I had been shooting California Magnum paintballs (nicknamed California marbles because they got that hard if you left them sitting around for too long). They fit my stock .6875 barrel quite nicely and were very accurate. The next time out we were shooting RP Scherer Premium. I couldn't hit the broad side of a barn at 20 paces it seemed. That is when I changed barrels and discovered the California Magnums fit the small bore just right and the RPS fit the larger bore just right (the RPS was tight as hell in the small bore). I immediately put the large bore barrel on and went out on the field and played with the RPS. Accuracy was back and I was shooting darts again.

I tried the different balls in both barrels again and it was always the same results. Small balls work better in small bore and larger balls work better in larger bore.

[echoes]

Originally posted by athomas
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.

Ah, yes, well those are the conditions I was assuming for this situation. As is often the case, what ideally should happen is not what actually does happen.

[hitech]

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.

My stroker has a VERY tight barrel. It shot PMI premium just fine, with NO barrel breaks. The fit is so tight that I had a hard time pushing the paintball back out after testing the "match".

Originally posted by FooTemps
A hard, paper thin, gelatain shell...

A paintball shell is a "little" thicker than paper.

[hitech]

Originally posted by athomas
In a barrel that is too small, the frictional forces are inconsistent and dependent on how the ball sits in the barrel.

Why? What makes it less likely to be inconsistent in a tight barrel. My experence is the opposite, if at all.

[FatMan]

Originally posted by hitech


Why? What makes it less likely to be inconsistent in a tight barrel. My experence is the opposite, if at all.

I believe the theory is that in a loose barrel, the ball does not contact the barrel wall on both sides of the ball (because the bore is too big for that). This could cause two things:

1) the ball rolls along one wall producing a spin - like it does in Tippman's flatline barrel

2) the ball bounces down the barrel hitting one side or another causing instability that will vary from shot to shot. Each time the ball hits a wall it robs it of a little speed - the number of times it does this and the exact place in the barrel will vary from shot to shot, so the muzzel velocity will vary from shot to shot, thus the ball will drop a little more or a little less from shot to shot and that is inaccuracy (as it is defined in paintball).

I believe AGD has run experiments with a coating inside a barrel showing the effect listed above. Still, experiments showing the resulting consistency would be interesting

FatMan

[bjjb99]

Warning, imperfect memory recall may have corrupted the following information:

I believe a long time ago, Action Pursuit Games performed a demonstration showing where paintballs contact a barrel. They sprayed a fine powder through a barrel to coat the insides and then fired a single ball. Upon removing the barrel, you could easily see where the ball contacted the barrel in the form of streaks. I could be mistaken, but I think the powder they used was an athlete's foot powder of some type.

I've got some paint that fits nicely in a barrel of mine, and also some paint that just rolls through. If I think about it next time I'm gonna fire my Mag, I'll spray some talcum powder down the barrel and put a round of each through to see the difference.

BJJB

[athomas]

Originally posted by hitech


Why? What makes it less likely to be inconsistent in a tight barrel. My experence is the opposite, if at all.

I think you meant less likely to be consistent so here goes.

In a large bore barrel the air is pushing just the mass of the ball. There are other factors affecting performance that were mentioned earlier but the overall frictional forces are not in play as much.

In a tight bore barrel the inconsistency comes from the imperfectly round paintball and the quality of the barrel surface and the paintball surface. When a shot is fired, these inconsistencies come into play as the ball moves down the barrel. There are more variables at play. A piece of debrise on a ball, extra lubricant on the ball, imperfections in the barrel or ball, fluctuations in chamber pressure, etc will have more of an affect in a tight bore than in a loose bore. As velocity increases, any slight increase in frictional forces are magnified.

[hitech]

Originally posted by athomas
...As velocity increases, any slight increase in frictional forces are magnified.

That is the part I do not agree with. Slight increases in friction cause slight changes in velocity. Since the diameter of paintballs is not consistent there will be the same degree of difference regardless. Actually a very loose bore that might have no friction on one ball and some on another seems like more of a problem. I challenge anyone to find a properly controlled study that shows barrel diameter to have any effect on accuracy.

[athomas]

Originally posted by hitech


That is the part I do not agree with. Slight increases in friction cause slight changes in velocity.

The equation is F = f * v^2

F = Resulting force
f = friction constant
v = velocity

The resulting F force counters the acceleration effects on the ball as it travels down the barrel and is directly proportional to the square of the velocity times the friction constant of the paintball/barrel. The frictional constant takes into account the pressure with which the ball contacts the surface of the barrel. Therefore increases in friction will be magnified as the ball increases in speed. Since the force F counters the acceleration it can actually result in deceleration at the end of the barrel by variances in frictional forces exaggerated by an extremely tight bore.

[echoes]

Yes, and that will hurt efficiency, but is there any conclusive evidence that it has a significant effect on accuracy?

[athomas]

In theory, if there is uneven friction on different sides of the ball, it will throw off the tragectory. This would be especially noticeable at the end of the barrel if gas were able to push one side of the ball easier than the other. It could induce spin or cause an immediate change in direction.

[hitech]

The differences in friction just aren't enough to matter. If the barrel is tight enough to make a significant difference then your going to have breakage problems. The difference between loose and tight makes very little difference in the pressure required to push the paintball to 300 fps. As for inducing spin from muzzle blast the pressure in the barrel is too low by the time the paintball reaches the end of the barrel. Maybe if the barrel was only 2 inches long, no porting. Even then, there is no evidence that the muzzle blast causes any decrease in accuracy.

To the best of my knowledge, no one has been able to prove that any of this makes any difference in accuracy.

[echoes]

Originally posted by athomas
In theory, if there is uneven friction on different sides of the ball, it will throw off the tragectory.

Right, the question is, what effect does the paint barrel match have on that? It could easily be tested by anyone who has any two identical barrels for the same gun, just with different ID's (like the Freak, Lapco bigshot/autospirit, etc), I'd really like to see the results of that.

[athomas]

For a test like that you shouldn't use a vented barrel. The venting helps compensate for some of the imperfections. Use nonported barrels of equal length.

I'll have to dig out my old 12" non-ported barrels and get some large and small bore paintballs. The 12" barrels were identical except for different id. Ten years ago I showed people the effects and they were obvious enough to see without written test data. I'll see if I can get my equipment set up and do the test again and write the data down this time.

[echoes]

Originally posted by athomas
get some large and small bore paintballs.

Yeah, but doing it with one barrel and several sizes of paint instead of 2 barrels with one batch of paint isn't as consistent. What I mean is that a Lapco Bigshot is more similar to a Lapco Autospirit than Diablo Blaze is to Diablo Hellfire. (different size, as well as different shells, fills, etc, and of course paint is just very inconsistent in it's size anyways).