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Old 11-26-2012, 02:41 PM   #21 (permalink)
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So, yes, if you take all that above, you can get a decent factor of shots per cu. in. at a particular pressure. 23 @ 4k is a pretty efficient.

For mags, we usually say 10/cu. in. on a 3k fill, 15/cu. in. on a 4.5k fill. If you fill in between, you can interpolate. It's not exact, but as close as you can go without testing a particular marker setup.

If you are looking at energy, your air use will go up with the square of the velocity, so 300 fps uses about 40% more air over 250 fps. But that assumes your barrel is the optimum length for your air pulse in both cases and your losses from your bolt and boring don't change (they will).

In the end, if you keep track of it all, you'll get a good idea of how that marker responds to different paint sizes, barrel lengths, and tuning. Then you can try to get more efficiency, or trade it for other performance factors.
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Old 11-26-2012, 02:43 PM   #22 (permalink)
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Put tank on gun. "Empty" it. Weigh it.

Fill tank. Let it reach a stable temperature. Weigh it.

Fire off enough shots to make an appreciable change on your scale.

Weigh it again.

Do math.

Someone please explain why this wouldn't be an appropriate efficiency test. Preferably using math.
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Old 11-26-2012, 04:01 PM   #23 (permalink)
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Quote:
Originally Posted by GoatBoy View Post
Put tank on gun. "Empty" it. Weigh it.

Fill tank. Let it reach a stable temperature. Weigh it.

Fire off enough shots to make an appreciable change on your scale.

Weigh it again.

Do math.

Someone please explain why this wouldn't be an appropriate efficiency test. Preferably using math.

In short,

a 68/4500 holds about 11.8 scf, or about .9 lb in weight. If you are looking for +/- 1 shot per cu over 68 cu, expecting about 20, you need to be able to see a change of one part in 1360. For a scale to hold the tank and air with a full scale of 3 lbs, its expensive to find one that will read .0007 lbs or .01 oz.
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Old 11-26-2012, 04:49 PM   #24 (permalink)
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Should have stated I wouldn't try to extrapolate anything. Based on practical experience, you can't simply calculate shot change at significantly different pressures. System efficiency changes too much.

Compare the energy in a tank at 4500psi, 3000psi and 1000psi and how that relates to Spider's data.

There's 80% more energy in a 4.5k tank than a 3k tank if your bottom limit is 1k, yet a mag's shot count only increases 50%. Efficiency is decreasing as input pressure increases, typical due to regulators. Energy in a 4.5k fill is 375% that of a 2k fill with the same 1k bottom! How many shots shots per ci do mags get at 2kpsi?

As Spider stated, you'll need to get a rough approximation from other players using the same setup or do your own testing. Sorry.

The best efficiency setups I could think of were posted on Punkworks. Unfortunately like most of my posts, they are now missing.

Ideally you would measure:
- Tank pressure change
- Tank volume (measured)
- Ball mass
- Ball velocity
The ball mass and velocity would indicate energy expelled while the tank volume and pressure change would indicate energy consumed. You could use average ball mass without having any effect on the calculations. Measure a counted 1000 balls and divide by 1000. Unfortunately you can't just measure average velocity for the reasons Spider mentioned. Each shot velocity will need recorded. This is especially important on guns that slowly drop velocity or significantly drop velocity when fired at high rates of fire.

This setup could be improved if the pressure sensor was accurate enough (do-able). It could yield an efficiency data point for each shot or every x shots. You could then incorporate/automate the entire thing so it generates a graph of system efficiency versus velocity/tank pressure/fire rate/number of shots since lube/etc on the fly as you play. Swap regulators, tanks, barrels, etc.

P.S. If anyone is interested in purchasing said setup, contact me.

Last edited by P0E; 11-26-2012 at 04:53 PM.
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Old 11-26-2012, 06:01 PM   #25 (permalink)
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heinous, I don't understand how an inefficient, hastily designed to be cheaply made compressor would increase system efficiency at all.
i was trying to confuse him more
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Old 11-26-2012, 07:04 PM   #26 (permalink)
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The easy way is to graph shot# vs pressure PSI in xcell or open office calc.

Then fit an equation to the curve, you could probably check your calculation against this and come up with a "gun constant" that would plug in.

I would also expect the curve to knee near the pressure of the high pressure regulator.
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Old 11-26-2012, 07:18 PM   #27 (permalink)
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The easy way is to graph shot# vs pressure PSI in xcell or open office calc.

Then fit an equation to the curve, you could probably check your calculation against this and come up with a "gun constant" that would plug in.

I would also expect the curve to knee near the pressure of the high pressure regulator.
If you add a calculated column for P0E's ln(P1/P2) factor, you can include it in the built-in linear regression solution and see if that fits better. That would be a pod's worth, and would explain why most of our estimates are "+/- a pod."
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Old 11-26-2012, 07:45 PM   #28 (permalink)
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i'm surprised paint is even consistent enough for this kind of math to be done. if i was doing it on my own i would just monitor my paint use vs psi in tank and plot a graph instead of using formulas.
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Old 11-26-2012, 08:55 PM   #29 (permalink)
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Originally Posted by Spider! View Post
In short,

a 68/4500 holds about 11.8 scf, or about .9 lb in weight. If you are looking for +/- 1 shot per cu over 68 cu, expecting about 20, you need to be able to see a change of one part in 1360. For a scale to hold the tank and air with a full scale of 3 lbs, its expensive to find one that will read .0007 lbs or .01 oz.
Itís not necessary to literally use a 68/45 to test the efficiency of a gun. A 13ci would work, so would a 22ci, etc., so long as you could fit it on the scale and get enough shots to move it appreciably.

Itís easy to get a scale which has gram accuracy (0.035 oz). Easily cheaper than a ďTechT Optimus GaugeĒ, or whatever else people are trying to sell.

The tank has a measurable mass of air inside of it.

The gun fires a carefully metered mass of air out the front. It better.

You can easily know what the weight of the setup is when full.

You can easily know what the weight of the setup is when the pressure is too low to operate.

Subtract, divide. No expensive gauges or setups or whatever required.

We're looking at averages anyways, so say you take 100 shots, and your change in weight was 24g.

That means you got about .24g of air consumed per shot. Yeah, itís a little off. But I think itís a reasonable ballpark. And people can take more shots/get a better scale if they want. So on a certain gun, .24g of air consumption equated to about 1500 equivalent shots off a full 68/45.
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He posts videos of himself on Youtube never leaving the furthest back bunker.
Even when playing against rental noobs, he is immobilized.
Logic and reason are anathema to him; but this does not deter him from prattling on.
He is the most interesting player in the world.
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Old 11-26-2012, 11:44 PM   #30 (permalink)
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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.
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