No offense taken. We are talking about the same thing...the exact terminology just gets academic. I see it as a 'path of least resistance' type thing. Altho the gas is expanding an all directions, most of it is going to go out the biggest hole. Things like path constrictions and changes of directions increase resistance to the flow (i.e. back pressure) and there's a bit of that in the power tube/valve assembly before it gets to the FVA. If it was a straight, unconstricted shot from the the valve to the to end of the powertube, I'm not sure there would be enough gas going out the side port to make the cyclone turn. So technically the system doesn't 'run' on back pressure, but I don't think it would work with out back pressure.

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QUOTE: Hwyman. If it was a straight, unconstricted shot from the the valve to the to end of the powertube, I'm not sure there would be enough gas going out the side port to make the cyclone turn. So technically the system doesn't 'run' on back pressure, but I don't think it would work with out back pressure.

I agree. You make an excellent point Hwyman! As designed, the a5 valve/power tube assembly provides a certain amount of back pressure in the air channel even without a FVA. Probably why some cyclones work well with no FVA while others see performance gains with the added back pressure the FVA can provide. In fact, I like the idea of having the FVA available to help tune the air delivery to the cyclone when reaching for extremely high rates of fire.
Again, point well made Hwyman.
Best regards,
Scoreshot

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Also, the measured turbulence using an fva is minimal. With a straight bore barrel, i'm +/- 8 fps all day long, and the majority of shots are +/- 5. What you want to do, is back out your RVA so it's almost flush with the powertube, then adjust your RVA so you're shooting right around 300, then go back to your FVA to get a final chrono. The reason why I run both, is it allows me more adjustability of my system. The RVA adjusts how long the air passage is open (ie how much air), the FVA controls how much of that air makes it to the ball. Finding a balance between the two is ideal. You can gain efficiency (shots per tank), as well as gentler shots on paintballs (good for brittle/tourney paint) and you can adjust it according to what you need/want at the time. Hope between me and scoreshot, that covers all the bases about this topic.

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Yep! Nice "cap" on the subject Raptor.
Your consistency looks great! Is that the "total variance" from highest to lowest fps or "deviation from the average" fps?

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Courage can exist only together with your fear.

it's total variance actually. I don't like using the standard deviation method, because I typically use very good paint which eliminates that straggler problem. I chrono at 300, and go from there. The last time I tested I shot 250 rounds, and all fell within +/-10 , 89% were within +/- 8, and 64% were within +/-5.

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You got a war face?!?LEMME SEE YOUR WAR FACE!!!

if i remeber your setup correctly you are running a LPK yes? do you set your pressure first, then w/ the FVA flush you bring your FPS to 300 and then fine tune w/ the FVA. i am using HPA so would this sequence be (in your opinion) the best way to "dial in" the a-5

I totally agree. My tests always reference total variance as well.
Nice work Raptor!

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Courage can exist only together with your fear.

nope, no lpk, but I am running a palmers inline reg (tank side of the line), set down to 725. Yes, with the reg set at 725, I will kind of bounce back and forth between the fva/rva and find a spot for each. On mine, typically, I have my rva about 2/3 to 3/4 out, stock spring, and the fva about 1 to 1-1/2 turns in past being flush. This gets me a chrono of around 270-275 which is ideal for my flatline (the fps that keeps the ball completely flat with no rise or drop over its usable range).

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You got a war face?!?LEMME SEE YOUR WAR FACE!!!

thanks a bunch to all! this really cleared up some confusion i had

look at how this seller describes the RVA vs. FVA issue. Seems contrary to all I have learnt here !
Tippmann A5 A-5 SIDE Velocity Finger Adjuster NO TOOLS! - eBay (item 360077186801 end time Aug-13-08 05:28:51 PDT)

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Speedball; choice of the Ritalin generation !