Copper Units of Pressure

O

Old Timer

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Was reviewing some load / powder data and paying particular attention to the pressures generated. I started visualizing the process in my head. But one thing I am not sure about. When the ( CUP ) transducer takes the reading at the case, I think? where is the projectile located. Is it still in the case, half way down the brl or about to exit the brl ?

OT
 
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I'm gonna take a guess and say that most likely it would vary depending on the powder and projectile being used and how efficent the cartridge is. Probably the burn rate of the powder would have the most effect on the pressure curve.
 
Its not a transducer

CUP is measured with a copper cylinder that is crushed by the pressure of firing. The copper cylinder is there for the whole ride. After the gun is fired the copper cylinder is measure to see how much it was crushed by the force of firing. There is no time element involved. The cylinder gets hit, deforms and is measured.

If you were using a transducer system (an electronic measuring device that converts strain to an electrical signal) you can get the pressure change over the entire time of firing. But it won't give you CUP - it gives PSI. Those are not the same measurements although they are both used to measure pressure. CUP and PSI are not interchangeable.
 
Cup/psi

Could one not say that 1.19PSI = 1CUP? Or would this be incorrect?
 
Cup

Well, I would think that there would be some type of trigger point in the barrel. Like a Piezo-Electric Transducer running into a Signal Amplifier.

I am just trying to figure out with a given amount of PSI generated by a specific powder, how long does the barrel need to be in order to use all the gas without belching out a lot of gas and causing the bullet to possibly tip.

Kind of the same principal as a gas port 2" from the crown. No more pressure when the bullet exits the barrel.

OT
 
Cup

CUP is only a mechanical means to measure maximum pressure. This is an old school method.
Now with the advent of transducers we can get real time pressure curves to be able to calculate where the bullet may be in it's progress down the barrel.
Rory
 
Old Timer said:
Could one not say that 1.19PSI = 1CUP? Or would this be incorrect?
Click to expand...

CUP and PSI can not be calculated from one another from everything I've read and data I've seen. For some reason CUP and PSI are pretty close with some cartridges and quite a bit different with others. I think that Alliant has some data in their loading pamphlet that shows both methods and how they differ. Pretty interesting and it'll make a guy scratch his head and turn to strong drink if he thinks about it too much.

Or maybe I'm just getting old. :)
 
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