The universal receiver ( a heavy duty single shot, lanyard fired, with a quick disconnect barrel arrangement) is the standard machine used for proof testing ammunition in the ammo makers labs. And the standard barrel length for the universal receiver is 30 inches. In the past the barrels were fitted with a copper cylinder system to indirectly measure chamber pressure. (the machines are now fitted with piezoelectric transducers.) Copper cylinder crusher method could give inconsisitencies, as the copper cylinder was crushed by a steel piston that pierced the chamber wall. After firing, the length of the compressed copper cylinder is measured, and the pressure required to do this is either calculated or read from a "crush chart". Just think how accurate the pressures are if the wrong alloy copper was used!! This is why you will see CUP listed in the pressures for the old system, such as 54,000 CUP. It is not the same as a true PSI reading. CUP is Copper Units of Pressure. True PSI is generally thought to be more than CUP, so our 54,000 CUP might actually be 61,000 PSI or more.

Way back when the 458 was developed, CUP was used, so who knows what the real pressures were? Could have been lower or higher than reported. Using the universal receiver and the CUP system required a substantial amount of operator skill. Something like not properly cleaning the chamber and the steel piston would give incorrect numbers.

So this is why many of the published velocities for ammo are higher than what we mortals obtain with our chornographs. Longer barrel generally equals a higher velocity, but not always.

Note to handloaders: If using old manuals, be aware of the CUP listings, the manual should explain this.