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Old 09-10-2006, 11:20 PM   #11 (permalink)
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Originally Posted by Wycke View Post
I've seen/heard that reported as well, but I don't buy it. The ball is accelerated by the pressure of the propellant (air or CO2) behind it in the barrel. Once it leaves the barrel, the air pressure is dissipated to the surrounding air and the ball begins to decelerate. Depending on the volume of the propellant, there could, theoretically be a final burst of acceleration as it exits the barrel immediately after the ball, though it wouldn't have any significant effect on the overall flight of the ball.

Smart Parts used this phenomenon as basis for their claims that their All American barrels were the most accurate. The second half of the barrel, just like the "front" of their freak barrels, was bored to .700. The spiral porting was purported (no pun intended) to direct or control the escape of this pressure, reducing the turbulence that the ball might experience as it left the tip of the barrel. Further, they claimed that the spiral arrangement of the ports imparted a spin on the ball to improve the accuracy of the shot. They never provided any scientific data to back up any of these claims, but at one point in time everyone and their mother had an AA on the field. Advertising is an extremely powerful tool.

In fact, I believe a few years ago that either Doc, Have Blue, or some other airsmith used a high-speed camera to capture the plume of vapor following a ball out of the tip of an AA barrel and also show that almost no vapor exited from the porting. I don't know if they also debunked the "spin" part of SP claims, though.
I seem to recall photos of baby powder blowing out ports. The phantom porting looked impressive. Then again, I suspect there was a pretty large margin of error going on, since another barrel(can't remember which) that I thought would "do well" simply from the design... didn't.

I think porting is a sound signature benefit only. That, and it looks cool.
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Old 09-10-2006, 11:56 PM   #12 (permalink)
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Once it leaves the barrel, the air pressure is dissipated to the surrounding air and the ball begins to decelerate.


Nope, not entirely. The air does actually maintain its pressure for some length beyond the end of a short barrel. While it does dissapate, i don't think it is enough to be entirely discounted. When you have air moving at 200 mph, it has a not-insignificant amount of inertia, and does not simply go away instantly. It keeps going the same way it was going, and therefore slamming into the ball (which is what, naturally, provides the motive force for the ball throughout the entire process).

Proof that the uncontained air will still accelerate the ball would be suspending a ping pong ball on a hair dryer, and those air cannons, that shoot nothing but a shockwave of air.

Note that the spurt of co2 from a blowback shooting liquid does not radiate from the end of the barrel in a sphere. It makes a cone, since the co2 doesnt want to change direction.

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I think porting is a sound signature benefit only. That, and it looks cool.

Seconded.
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Old 09-12-2006, 01:51 PM   #13 (permalink)
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I've read articles on this subject as well, and they are all very interesting. I'm surprised no one has written one as of late, because there is quite a bit that has changed since these ideas were floating around.

The article I read also referred to the length as what most would call the "control bore" these days (ie: length before the step or porting). According to this article, which I believe was in an APG back in the early to mid-90's, the most efficient barrel (not accurate) was in the 8-in range. Keep in mind that most markers of that day were operating on either straight CO2 (between 600 and 900psi) or mags that were regulated to operate between 600 and 700psi. The higher pressures could push a paintball up to 300fps in a shorter distance, so it was determined that 8-inches was about all that was necessary.

It also mentioned that markers operating on lower pressures (ie: autocockers running between 400-500psi) would require a slightly longer barrel to get the required velocity without a significant loss of efficiency. They stated that 10"-12" was best suited for these markers.

Classic Mags had stock barrels of 8-inches, Cockers came with 10-11 inch barrels, and PPS always keeps their markers in that same range of barrel lengths. But anymore, people are dropping the "expandable" CO2 for a more steady state compressed air, which debunks a lot of that theory. They are also less interested with efficiency and more interested in speed.

I agree with Sniper1rfa above. CO2 will continue to expand to the end of the barrel in a properly tuned marker and can maintain (if not slightly increase) the velocity for a longer distance than compressed air or CO2 that has already expanded completely before the barrel ends.

There are a lot of factors involved anymore. Anyone up to the challenge?

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Old 09-12-2006, 02:20 PM   #14 (permalink)
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I have no data to prove this, only my feelings and the feelings of other team mates at the time.

When I was sponsored by Freak - they gave us our choice of tips. I had many tips as well as many other players on my team.

Although length seemed to make little difference - the All American tip was noticible more accurate than the Freak tip. These tips differed in thier hole patterns and hole size.

Again, nothing scientific - but I would be willing to wager B's kidney on the results of a scientific test.

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Old 09-12-2006, 03:27 PM   #15 (permalink)
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The 8 inch guideline Glenn is refering to is a 8 inch un-ported barrel section to allow for the maximum expansion of CO2, it is more a matter of efficiency than acceleration and accuracy.
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Old 09-12-2006, 04:04 PM   #16 (permalink)
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I don't know about the rest of you guys but I'll be using a 12 inch unported barrel from Palmers probably the rest of my career. From my anecdotal evedence, non ported barrels are the most accurate out there.
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Old 09-12-2006, 04:16 PM   #17 (permalink)
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My personal favorite length is 10" ported.
Robertsr,
Do you have a PPS barrel on your Sniper/ cocker? How do you like it?
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Old 09-12-2006, 05:42 PM   #18 (permalink)
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man why am I always the engineer that steps up to the plate in these situations?

Okay looking at post barrel ball acceleration.... you basically have a vessel that is containing pressure (the ball and barrel) The size of the vessel is increasing at an increasing rate (acceleration of ball forward).. as the size of the vessel increases the pressure decreases... once the ball is free of the muzzle of the barrel you no longer have a contained vessel, so the pressure 0 (gauge), but you still have molucules of CO2, HPA (no longer hpa) moving/expanding in a linear manner for a short distance until they loose their energy (we see this as the "clouds" of CO2 on cold days)... Now because we have the ball free of the barrel (and friction) and there is still some energy acting on the ball from the gas continuing to expand then you may see some additional acceleration... but what ever you see will be nominal. I think a lot of companies may be marketing on this theory.. and not on anything measurable..mainly because it's easier to say it's happening and have the theory in your back pocket... than it is to show that it is happening (it would cost more than their marketing budget to prove what is happening in that 1/4" away from the muzzle of the barrel).

The science part, I'm pretty sure we can substantiate the theary, I know there are a few other physic geeks here that will probably agree with what I said... it's the actually physically proving of the "post barrel" acceleration that is damn near impossible due to lack of proper tools on my end.

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Old 09-12-2006, 06:07 PM   #19 (permalink)
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In my possesion I have all kinds of barrels, short, long, ported, unported, rifled and whatever else there is. (ramrod LOL)

I personally have found that some short barrels shoot a lower velocity than when I put on a longer barrel with the same inside ID.
I guess this would be due to the wasted gas syndrom. A longer barrel lets the ball take full advantage of the expanding gases. (especially liquid Co2)

However, my favorite barrel, in my humble opinion, is my 14" bushmaster SI barrel. No bells, whistles, just smoooooth. And in the same breath my 18" bushmaster barrel is the worst.
Go figure.
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Old 09-12-2006, 06:42 PM   #20 (permalink)
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Quote:
Originally Posted by Schmitti View Post
man why am I always the engineer that steps up to the plate in these situations?

Okay looking at post barrel ball acceleration.... you basically have a vessel that is containing pressure (the ball and barrel) The size of the vessel is increasing at an increasing rate (acceleration of ball forward).. as the size of the vessel increases the pressure decreases... once the ball is free of the muzzle of the barrel you no longer have a contained vessel, so the pressure 0 (gauge), but you still have molucules of CO2, HPA (no longer hpa) moving/expanding in a linear manner for a short distance until they loose their energy (we see this as the "clouds" of CO2 on cold days)... Now because we have the ball free of the barrel (and friction) and there is still some energy acting on the ball from the gas continuing to expand then you may see some additional acceleration... but what ever you see will be nominal. I think a lot of companies may be marketing on this theory.. and not on anything measurable..mainly because it's easier to say it's happening and have the theory in your back pocket... than it is to show that it is happening (it would cost more than their marketing budget to prove what is happening in that 1/4" away from the muzzle of the barrel).

The science part, I'm pretty sure we can substantiate the theary, I know there are a few other physic geeks here that will probably agree with what I said... it's the actually physically proving of the "post barrel" acceleration that is damn near impossible due to lack of proper tools on my end.

E
Agreed. While not based on anything but my gut feeling I don't think that the uncontained (or unchanneled, maybe) energy will have any major effect on the ball. If anything I'd guess that the randomness of the expansion would mess up the accuracy if anything.

Of course,t he main reason I've never bought into that was how long would this effect last? Maybe an inch? How far out do you chrono? A foot? So by the time you're measiuring the velocity and tuning the gun the ball would have stopped accelerating (actually, it's just negative acceleration , but I digress).

Oh, and I like 12" barrels for aiming reasons. I've always kinda thought that a smooth tube is a smooth tube ( other than paint to barrel match). I have seen massive differences in consistency while matching paint, I've had cheap paint do +/-20 out of one barrel and +/- 10 out of another. Since I believe that consistency and paint are the two biggest factors in accuracy I think the "barrel match" crowd may actually be on to something. Of course, IIRC one day I had better consistency with a 'bad' paint to barrel match (loose) versus the tight fit so I went with the loose fit, better consistency with a little efficiency hit.

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