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Old 11-27-2012, 04:04 AM   #31 (permalink)
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Originally Posted by the_chemist View Post
You're right, mass is a much better method than pressure. We should get a list of different volume/pressure tanks together that has the masses of air they hold at different fills. "empty" would be when there is 200 psi or so.
You technically don't really need a list.

All of that should be calculated easily.

Unless you can't trust the published internal volumes of tanks.

*cough* Guerrilla Air *cough*

That's a topic for another thread.

"Empty" PSI will vary by marker. I set mine to about 600 for calculations.
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Old 11-27-2012, 04:34 AM   #32 (permalink)
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Old 11-27-2012, 10:35 AM   #33 (permalink)
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Quote:
Originally Posted by GoatBoy View Post
You technically don't really need a list.

All of that should be calculated easily.

Unless you can't trust the published internal volumes of tanks.

*cough* Guerrilla Air *cough*

That's a topic for another thread.

"Empty" PSI will vary by marker. I set mine to about 600 for calculations.
There is the issue of compressibility. But yeah you can calculate it. The only issue with using mass, is that it is inconvenient

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Old 11-28-2012, 02:08 PM   #34 (permalink)
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Calculating for efficiency is more useful than "shots per x,y,z". Similar to how MPG is more a useful a stat than gallons consumed on a trip of x miles.

Graphing efficiency as you empty a tank is significantly more useful than just obtaining the average efficiency for the entire tank range. Most modifications do not merely offset the graph up/down. They tend to increase performance at one pressure while decreasing performance at another.

Measuring mass favors larger tanks while measuring pressure favors smaller tanks. Measuring mass is also more cumbersome, it takes significantly longer to graph efficiency and makes graphing efficiency while playing impossible. Consider a 13ci tank while measuring pressure changes. Each shot drops tank pressure a significant amount compared to a 68ci. Therefore a less critical gauge/sensor can be used. Fewer shots need fired as well. A very accurate mass system prefers a large tank which therefore requires more shots.

I would argue the compressibility has very little impact on any efficiency or fill/volume/pressure correlation calculations. In the above examples, the mag's system efficiency change was an order of magnitude greater than the compressability. This isn't a scientific experiment. We are simply doing some back of the napkin stuff using measurements that are easily +/-5% and operating under the assumption that our results will easily vary that amount.

heinous,
Paint is adequate because of what we are doing and how paint variations relate to the energy equation.

We are looking at maximum theoretical energy potential and comparing that to useful energy out. Any energy lost in the gun's operating system, lost to friction or turbulent air, energy imparted to spinning the ball, etc, etc,.. Doesn't matter, it's all put in the same category, inefficiency.

Paint ball mass and velocity are the only two things that relate to 'useful energy out'. Velocity is easily measured. So if our gun system has a hard time with lumpy paint and fires it at a lower velocity.. well that shows up as a less efficient system because that's what it is. A gun system that can fire lumpy paint without a reduction in velocity will show up as a more efficient system.

Regarding irregular paint mass...
The calculation useful energy out is E=0.5mv^2. Since m has a power of only 1, we do not need to measure the mass of each ball. The average paint ball mass is adequate even if there's a large ball-ball variation. Try it for yourself with the following two data sets.

3g 100fps, 3g 200fps, 3g 300fps, 3g 400fps
vs
2g 100fps, 4g 200fps, 1g 300fps, 5g 400fps

You should notice equal total energy even though the mass fluctuates in the bottom set.
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Old 12-06-2012, 11:23 AM   #35 (permalink)
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Please.....continue!
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Old 12-06-2012, 11:48 AM   #36 (permalink)
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I'm not much for math but couldn't you just fill the tank and count how many shots you get before the velocity drops off? Wouldn't that tell you how many shots per that particular tank you get.
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Old 12-06-2012, 12:04 PM   #37 (permalink)
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You certainly could. The downside is you'd have to shoot the tank dry and all the paint that entails. Half a case? More?
My measuring and doing the math, you can find how much air is used for a given number of shots and then extrapolate it over the whole tank.
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Old 12-06-2012, 12:18 PM   #38 (permalink)
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Good point. I guess to a degree I'm spoiled having never used anything bigger than a 13cuin.its a simple thing to empty that.
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Old 12-06-2012, 04:02 PM   #39 (permalink)
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Sorry, I didnt notice if this thread was stickied or not. If not....PLEASE do. The different thoughts and ideas are just killer.....
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Old 12-07-2012, 12:17 AM   #40 (permalink)
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Quote:
Originally Posted by Keebler View Post
Good point. I guess to a degree I'm spoiled having never used anything bigger than a 13cuin.its a simple thing to empty that.
Shooting empty a big tank is surely a waste of money and time... although too small and your data resolution is too coarse. 13ci is good.

Unfortunately there's other data needed to make the shot count relevant.

Paintball mass changes a good amount. Even with the same manufacturer and brand. Hell even within a batch. It's not uncommon for mass and therefore shot count to vary 8%.

Second is how large a role velocity plays. The formula for projectile energy is one half mass times the square of velocity. Energy changes directly with mass, but by the square of velocity. So a marker with no change to anything but paint, can double its shot count just by reducing velocity from 299FPS to 211FPS. Most efficiency tests with 12g are misleading because of this very reason.

For example. Marker A starts at 280FPS, ends at 220FPS and gets 30 shots per 12g. Marker B starts and ends at 280FPS, but only gets 25 shots. Marker A isn't necessarily more efficient. If you were to adjust Marker B's velocity to 220FPS (since that's apparently an acceptable velocity) then you might see 40 shots per 12g.

Finally, the gas source isn't well regulated. CO2 bottle fills are the worst, even factory filled 12g CO2 cartridges aren't great. HPA has an issue with hot fills. This heat from filling artificially/temporarily increases pressure and apparent energy of the tank which results in lower than potential tank energy. Tank surface cools off before the gas inside so even if the tank is at ambient, the air temp might be elevated.

Manufacturers like Bob Long could hypothetically exploit these factors.
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