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Old 01-02-2004, 08:42 PM #43
daishi
 
 
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Another question to think about... how does the barrel affect this? I mean you said "Kinetic Energy at the muzzle = potential energy from the gas", right? If a 10" barrel with no porting shoots 280fps, then you stick on a 16" with lots of porting, you'll have to increase the air usage, but the equation doesn't factor this in, correct?
The equation does factor this in only when you reach the desired fps and know the input pressure. Each barrel would cause a change in the fps at a constant input pressure. Therefore to update the equation for differing barrels you would need to adjust the input pressure value in the equation to account for this (assuming you keep the fps the same). I don't see how it would be possible to do otherwise myself. Maybe CQ or electrician would have an idea.
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Old 01-03-2004, 12:02 AM #44
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But if you're only adjusting the velocity through the IVG instead of the input pressure, then the input pressure is the same, you're just using more air. How does that not throw off the equation? I mean, wouldn't we have to come up with a new equation that would factor in how long the valve is open?
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Old 01-03-2004, 12:29 AM #45
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Well, you must remember that a properly set cocker doesn't use the IVG to adjust velocity at all (well, that's mostly true... read on). Using the IVG is wrong from the start and so we shouldn't worry about figuring out equations for such a situation.

As to the barrel, you're absolutely right, kindof. When I said "Kinetic Energy at the muzzle = potential energy from the gas" I was assuming a 100% efficient gun to find the theoretical max # of shots on a tank, which means a 100% efficient barrel. If you then use a barrel which is not 100% efficient (ie, a real one ) then that statement no longer holds true.

Daishi is not quite right in saying the equation accounts for this, but I think I see where he's coming from. Say you slap on a very inefficient barrel. You then have to raise the input pressure to account for the loss in efficiency, to get the ball properly up to speed. This has a twofold effect. First, it raises the minimum tank pressure needed to shoot a ball at full velocity, thus reducing the number of full-speed shots you can get from your bottle. Second, it shortens the valve dwell, which will usually lower velocity. The result is that you have to adjust spring pressure to work with the new operating pressure, and you have to balance these two forces every time you change the barrel. We call this procedure "sweetspotting." Sound familiar?

Technically, even changing paint-barrel match requires re-sweetspotting the gun for maximum efficiency to balance the forces of input pressure and forced valve dwell due to hammer momentum and spring balance. Of course, no one wants to sit in the staging area working on a marker every time they change their Freak insert, so the "quick and dirty" method is what most of us do at the chrono - either change input pressure or IVG tension but usually not both. It gets us an acceptable result in less time.

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Old 01-03-2004, 01:01 AM #46
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Hmm.. I see what you're saying. Personally, I just sweetspot my marker, then when I go to the field next, I crono the marker and if it's too low, I re-sweetspot the marker with how it's currently set up, starting with the reg. Usually doesn't need much, if any adjustment though.
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Old 01-03-2004, 01:04 AM #47
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Very true... changing barrels doesn't affect the whole system so much that you'll see much change. I'm just being technical - "technically" sweetspotting after a barrel change will raise efficiency - but maybe only by 20 shots per tank if the barrel is still decent. It's theory vs. real-world.

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Old 01-03-2004, 01:09 AM #48
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Well, I have a Scepter kit, so my barrel is always the same, just depends on what insert I use with the paint (PMI Premium or GAP) and how well it fits.

That's the problem with some people though, when you show them numbers they say "yea, but that's all theoretical, not real-world" ... what they don't understand is the theoretical is usually the best case senario. I mean, granted the Excel spreadsheet I made computes for 100% theoretical efficiency, when I showed it to the people at wgppress they started talking about how inaccurate it was. I'm still waiting on my reply of "of course it's inaccurate, this is at 100% efficiency without air used to recock the marker... you're going to get much less than these numbers"
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Old 01-03-2004, 01:11 AM #49
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That's also why the closed bolt vs. open bolt myth persists - for every intelligent person who points out that any difference in range or accuracy defies the laws of the universe, there's a hack who refuses to agree, citing his brother's cocker which seemed to shoot much further than his mag last week at the field during games.

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Old 01-03-2004, 01:51 PM #50
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CQ that's exactly what I was trying to say, just at 2 AM so I was pretty tired. A 100% efficient barrel every time wouldn't affect the system for overall efficiency. It's when you drop to a less efficienct barrel that you would then start to see variances in your shot per tank values.

Now, theoretically, you would still have the same efficiency on a barrel kit as long as you keep the same consitancy in paint to barrel matching, so in that sense you wouldn't change the efficiency of the gun. It's when you put in that .690 insert for a .684 paint size that you'd throw off your numbers. At least that's what I'm picturing here.
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Old 01-03-2004, 02:33 PM #51
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Very true. Of course, the difference in mass of a .684 paintball vs a .688 paintball also affects your theoretical max efficiency.

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Old 01-03-2004, 03:10 PM #52
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The difference in paint weight I hadn't thought of. A change from 3.23 to 3.03 is about 152 shots, but like I said on the other board, if you were to calculate a 68/4500 at 290fps at 300psi you get around 2,800 shots, which is unheard of. Even with really tinkered with cockers, I haven't heard of much past 2,000. So you're losing quite a bit from efficiency.
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Old 01-03-2004, 03:27 PM #53
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Even AKA guns don't quite hit 80% efficient. Most cockers are below 70% efficient (Josh did the math for these two numbers a long time ago). Even the noise of the marker is wasted energy. Each little puff of air, every port in the barrel, every little bit of turbulence in the gas path, every imperfect seal, etc. all reduce your efficiency.

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Old 01-04-2004, 01:36 AM #54
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Not only is weight a factor, but you'd have to weigh each type of paint, even those of the same size as density of the fill will vary from one company to the next, not to mention winter vs. summer fill. Take this into account and we've just added another can of worms to the mix.
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Old 01-04-2004, 02:42 PM #55
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Well, there are dozens of factors we haven't taken into account. Ambient temperature, ambient air density, lattitude and longitude, the tides, the phase of the moon, Jupiter's position in the sky, whether or not you've made all the requisite sacrifices to your cocker gnomes, etc.

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Old 01-05-2004, 12:32 AM #56
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haha it'll be easier to figure out how to hit the flag on the moon with a baseball then figure out the efficiency of a gun hahaha.
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Old 01-05-2004, 04:14 PM #57
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Quote:
Originally posted by daishi
Not only is weight a factor, but you'd have to weigh each type of paint, even those of the same size as density of the fill will vary from one company to the next, not to mention winter vs. summer fill. Take this into account and we've just added another can of worms to the mix.
Very true. Imagine the jump in sales if it was discovered that Hellfire allows 200 more shots per tank than RP Premium!

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Old 01-05-2004, 04:22 PM #58
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Most of this stuff is more than a bit over my head, but wouldn't a heavier paintball go further than a lighter paintball assuming they both had the same initial velocity?
Of course the heavier paintball would require more energy to achieve this velocity, but wouldn't the extra mass give it more inertia?
Just a question, if I am completely wrong don't slam me too bad.
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Old 01-06-2004, 03:37 PM #59
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Yes, that's absolutely right. A heavier paintball will generally travel further, as long as its increase in weight doesn't correspond to a big change in size.

However, bigger paintballs are also bad for efficiency, since as you said, it takes more energy to get them up to that same initial velocity.

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