Need conversion formula, PLEASE HELP!!!!!

[waco]

Can anyone PLEASE tell me how to convert C.U.P. to P.S.I.?

I see some much conflicting info on the net. Some formulas that don't seem to work, and others that say it just can't be done....

What is the deal?

I need an EASY way to convert these numbers. Is it possible?

Thanks in advance guys.

Waco

[geargnasher]

Copper Units of Pressure are derived from the original, standardized method of using a universal receiver with a tap into the chamber and a copper pellet that got deformed x amount under x pressure. PSI is just that, Pounds per Square Inch, measured with a piezo-electric strain gauge that detects stretch in metal. The copper crusher could measure peak pressure, but that was it. The strain gauge data can be mapped and with one a trained person can discover potentially dangerous anomalies in the recorded time/pressure curves. The piezo data tells a more complete story and has been the reason a lot of published data has been revised or deleted.

The difference between peak pressure and pressure duration is why the two methods of measurement don't translate between each other very well. They are measuring the same thing, but not in the same way.

Gear

[waco]

Good enough. Thank you.

[bhn22]

Cliffs Notes: They're not on the same scale, and don't translate directly to each other. Why? read above.

I think I need to go to bed now, I'm babbling....

[mpmarty]

In the "old days" there was CUP and LUP. CUP was used for rifle rounds at rather high pressure. LUP was Lead Units of Pressure where lead was compressed instead of copper and was used for low pressure loads like in pistols. Now we have the magic of transducers that act as strain gauges and come with tare tables to translate readings into PSi or pounds per square inch. All measure pressure but in different ways and ARE NOT TRANSLATABLE from one to another.

[bhn22]

I completely forgot about LUP. It went out of use before I started loading.

Marty- you're dating yourself!

[MtGun44]

Well said, Gear!

There are various "sorta useful" comparisons, but since one is a real measure of instantaneous pressure,
and the other is more like a measure of the peak pulse pressure - but with some mechanical and inertial
delays, errors and non-linearities built it - they really are different enough that the real experts say,
"Just don't try".

There are some rules of thumb out there, and they can be useful, but really, just stick with the loading
book info and believe it. Many folks are convinced that lawsuits and fear are causing many "well known
to be safe" old loads to be declared too high pressure and reset lower. In some cases, I believe the
actual SAAMI pressures for some rounds are now lower than they used to be, but in most cases, the
issue is that the old loads were really well above the design pressure for the cartridge, and we got away
with it only because we were 'living on the safety margin'. Current electronic pressure measurement
systems are far more accurate, and mostly the powder makers publishing are giving the straight
story, not 'dumbing down the data'.

Bill

[44man]

Common problem today with manuals and load info showing one or the other, still a lot of CUP readings being shown.
LUP was mostly shotguns and is still shown that way.

[waco]

The reason I was asking is because of the formula in the "modern reloading second edition"
For reducing jacketed load data for cast to match the BHN of your alloy.
The formula only works with PSI, not CUP.
There are loads in other manuals I wanted to know the PSI but they are in CUP.

[runfiverun]

LUP is being changed over to BAR in the shotgun stuff.
so you gotta pay real attention there as to which system is being used if you think about making a change in a load.
plus add in the new 3-1/2" shotguns/shells which are rated to a higher pressure, and you can see how things could get confusing.

[geargnasher]

The reason I was asking is because of the formula in the "modern reloading second edition"
For reducing jacketed load data for cast to match the BHN of your alloy.
The formula only works with PSI, not CUP.
There are loads in other manuals I wanted to know the PSI but they are in CUP.

I figured that and have run into the same problem. For example, try to reduce a powder that isn't listed in Modern Reloading, and for which there is no published PSI data. When you run into these things often enough (as I have), we should both take my advice and buy Quickload.

One thing I forgot to mention that Bill did was inertia. The drawback to the copper crusher is it only takes the highest measurement that is sustained long enough to deform the pellet. There can be spikes in pressure before or after the peak that exceed the maximum pressure recorded by the pellet, but whose duration is too short to overcome the inertia of the punch or pellet. The spike is still stressing the gun steel. SEE is one thing a copper crusher won't see until it's at a dangerous level, but a pressure/time map can indicate secondary disturbances that are the precursors of bad things.

Gear

[waco]

Quick load...... I'll look into that.
Thanks Gear.

[felix]

Remember always that published specs about any ammo is from "guns" specifically set up for testing (unless otherwise stated). This means the ammo was fired in guns that are typically strong enough to not destroy themselves via many extreme loads, and these guns are no way commensurate with the guns typically shot at home. Extrapolation of this idea would indicate a 40K psi industrial load would possibly be equivalent to a 35K load in a rear-locking lever gun. So, if a load is 40K book max, assume that same load would be an overload (over time) in your cowboy gun set up for the 35K max. Some time ago, for example, I read that Marlin proofed their barrels at 80K PSI, giving a realistic safety margin for repetitive 35K loads. However, that does NOT speak for their ACTION (locking) arrangement. In other words, always beware or be aware of what is published. ... felix

[44man]

Gear and Felix are so correct. This is a very tough thing today.
Notice loads have been reduced because many times peak was not at the copper crusher. Think of the thousands and thousands of loads we shot long ago without harm.
Look at how long it took to find REDUCED loads of slow powder can be worse then over loads.