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Old 11-25-2012, 12:37 AM   #1 (permalink)
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Automag Volume Help

A'ight. From some research, I've come up with this info. Can someone please verify or deny this? I'm not trying to make any statements, just trying to figure out if this is true.

A mag dump chamber fills to a certain PSI before its sealed off, and eventually is used to push the ball down the barrel.

Aside: Perfect paintballs at 280 FPS shoots the same irregardless of pressure, pressure does not affect distance...


Therefore, increasing the volume of a mag dump chamber (magic box?) theoretically fills the mag dump chamber to the same PSI, but with more air. Therefore, the shot would feel "softer" but at the cost of poor efficiency.

Therefore, decreasing the volume of a mag dump chamber (hypermag?) theoretically fills the mag dump chamber to the same PSI, but with less air. Therefore, the shot would feel "harder" but at the benefit of efficiency.

Does this sound right? Or does air being at a lower pressure / higher pressure not affect efficiency in the least?

Thanks!

Last edited by Otter; 11-25-2012 at 12:40 AM.
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Old 11-25-2012, 12:41 PM   #2 (permalink)
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Quote:
Originally Posted by Otter View Post

Aside: Perfect paintballs at 280 FPS shoots the same irregardless of pressure, pressure does not affect distance...
You're kind of over constrained there. Yes 280 is 280. However, all things being equal in a mag, higher dump chamber pressure means more air going out the barrel (and more velocity). Since the air doesn't help close the valve like a sheridan or nelson, higher pressure is always more volume out.

With air and a fixed dump chamber, you can use ideal gas laws.

P1V1 = P2V2

That's the calculation at the beginning and end. In the middle is the gas leaving the chamber and going through various restrictions and leaks. TK measured the pressure immediately behind the ball on a level 7 at about 60 psi. There are other dynamics involved, but that gives you an idea of what the burst of air is doing.

The equation above says that you need a certain amount of pressure and volume together to equal what you spend on a single shot. The magic box trades more volume for less pressure. The problem with lower pressure is that it can be too low. Most acceleration occurs near the bolt face, so as you try to launch with lower and lower pressures, you can't push enough air through the power tube to keep up with the expanding volume behind the ball and your losses around the ball and out of the feed neck.

With a longer barrel on a magic box mag, you might be able to keep close to the usual efficiency of a mag with the lighter ball pressure. With flow dynamics, your pressure is proportional to the square root of the flow volume. As you jack the pressure up, you're not getting proportionally higher flow. This means that you can increase the pressure behind the ball, and your leaks around the ball and bolt will not increase proportionally. The converse is also true. As you lower your pressure, the leaks will take a larger portion of your air mass.
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Old 11-25-2012, 09:46 PM   #3 (permalink)
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the pressure in the dump chamber was changed because of the magic box. it had more volume and less pressure..this is where the efficiency insert comes in. we reduced the dump chamber and increased the pressure so that they totaled the same as before.this allowed us to increase efficiency. i think that is where you were going with this.
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Old 11-26-2012, 08:12 AM   #4 (permalink)
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Spider, that was a great post. I've read it three times now, but still had to wait till morning to comprehend it fully.

Super, you have the right direction. I'm thinking about the effects off the increased pressure and lowered volume. Mainly insofar as the force hitting the paintball, especially in the winter.
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Old 11-26-2012, 08:27 AM   #5 (permalink)
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edit: never mind, i read it over. you were turning the reg down.

Last edited by heinous; 11-26-2012 at 08:57 AM.
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Old 11-26-2012, 11:08 AM   #6 (permalink)
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edit: never mind, i read it over. you were turning the reg down.
Thinking about de-volumizing?

That's what I usually think of in these discussions. It has a more obvious effect between HPA and CO2 at least. The discussions about mag de-volumizing and high/low pressure 12g setups in other markers are all related. The thing about mags is that the valve behavior is mostly fixed, and changing the dump chamber volume is "magic".
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Old 11-26-2012, 06:45 PM   #7 (permalink)
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now i want an adjustable volume dump chamber...
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