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Old 09-06-2012, 07:24 AM   #31 (permalink)
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sorry to derail your thread spyder! I didn't bother trying to weigh my shells as my scale only registers grams. I would not have even gotten a measurement in the ranges you were talking about.

The springs inside my 2 shells are both the size of phantom valve springs but a little longer. possibly closer to a nelson valve spring.

One of the leaks I had was through the fill port. if I put my finger over the very tip you could feel the pressure. replacing that microscopic oring inside the tip of the stem sorted it. I didn't even realize the swollen part of the tip came off until it came loose while dissaasembling the back cap once.
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Old 09-06-2012, 09:28 AM   #32 (permalink)
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Quote:
Originally Posted by dukie View Post
sorry to derail your thread spyder! I didn't bother trying to weigh my shells as my scale only registers grams. I would not have even gotten a measurement in the ranges you were talking about.
It's all good actually. I was thinking of things to try to make a goblin work. The concept of a minimal marker is neat, but the goblin seems a little less than minimal. I'm wondering what a reliable, 260 fps goblin would look like, or if it would just be something else altogether.
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Old 09-06-2012, 10:06 AM   #33 (permalink)
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Based on the information provided by Dukie...

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Originally Posted by dukie View Post
The internal volume is ~.136 in^3
We need 200 cubic inch pounds of energy to launch a paintball at 300 fps (This is information from either Ynda or Yoda or one of the other thinkers here)

With these pieces of information we get:

200 cubic inch pounds = .136 cubic inches x ?? Pounds per square inch

When we solve for ?? We get ~1470.6 PSI

This explains why we are having issues making velocity. As co2 is around 800 PSI, and assuming a linear rate of fall in velocity based on pressure...

We are looking at a theorical maximum velocity of ~163.2 FPS. Obviously this is a flawed theory, as the amount of energy is not a linear progression and I am too lazy to look up the real physics to calculate this.

What we need is either a LOT more pressure or more volume.

Ty
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Old 09-06-2012, 03:12 PM   #34 (permalink)
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Here's the way I did the math:

200 in-lbs of potential energy is proportional to the kinetic energy of the ball.
200 = E = k*v^2
k is a constant comprised of the 1/2*mass term and efficiency losses. Using 300FPS as the velocity, k = .002222

The goblin shell contains 108.8 in-lbs of energy.
108.8 = k*v^2

Substituting the k from above in yields a velocity of 221.23FPS. Which seems to line up with real world results (which tend to be lower, but I think that is attributable to the short barrel length).

But yes, to get to 300FPS, it looks like you will need either 1470psi or .25in^3.
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Old 09-06-2012, 07:50 PM   #35 (permalink)
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You mathemagics are better than mine.

Ty
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Brass Freak compatible and Equation inserts in .665, .670, .675, .678, .680 and .685

Current Freak compatible inserts in stock:
.665 = 0, .670 = 16, .675 = 3, .678 = 4, .680 = 4, .682 = 4, .685 = 11

Still selling brass tubing, with .678 barrel stock now available!

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Old 09-06-2012, 08:10 PM   #36 (permalink)
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I believe that 200 in lb limit is suspect per my earlier post.
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