C.U.P. vs PSI

[outwesthunter]

Does anyone known a conversion between C.U.P. and psi? I can figure out that one c.u.p. is quite a bit larger than 1 psi. but how much?

[stubblejumper]

There is no such thing as a direct conversion from C.U.P. to PSI.

[johnch]

I have a older Lyman reloading manual and it states
1 C.U.P. should equil 1 P.S.I. but But that is usaly not the case....
The issue of witch method is more correct has been conveniently side steped by assigning different units of presure to each method .
because the 2 pressure testing methods test different peaks ,max pressure for each unit of pressure is different

I read most of the 12 pages of text and graphs
Long story made short ,lots of tec. talk ,no strait ansers,don't try to read 1 into the other .
After reading it ,it was as clear as mud.
IMO just follow what the reloading manual says for min and max

[stubblejumper]

IMO just follow what the reloading manual says for min and max

But never use a load that shows any signs of pressure even if the manual says that it is a safe load.Loading manuals are only guides and not to be taken as gospel.

[Slamfire]

Stick with psi, cup is full of inaccuracies, and requires an artist to interpret the signs into pressure. PSI is read directly off of a digital display and anyone can be as accurate as anyone else.

[driftrider]

I have a feeling that it won't be long before all the ballistic labs that do the load workups for the published manuals universally use PSI data. The cost of piezo-electric pressure barrels and equipment will drop, and SAMMI has already published PSI standards for most commercial cartridges. In addition to piezo-electric equipment (which is the best but rather expensive) there is the Oehler strain gauge pressure testing equipment available that allow reasonably accurate pressure readings to be taken from a factory rifle (in PSI of course).

One thing is for sure, PSI is PSI. It is a genuine, quantifiable unit is measurement for pressure that can be converted to any other absolute unit of pressure (i.e. atm, pascal, mmHg, inHg, barye, etc...). CUP, on the other hand, while being better than nothing, is hardly an accurate measure of absolute pressure and variations are rampant. That is why there is no conversion from PSI to CUP. If CUP were a genuine linear unit of measure, then converting from one to the other would be as simple as multiplying by a constant. But CUP isn't a definate measure of absolute pressure, and there is no constant difference between CUP and PSI, so there is no possible way to directly convert from one to the other. Published CUP pressures are virtually meaningless when comparing different cartridges, and only provide a relative pressure comparison between two different loads for the same cartridge.

Mike