Back to the beginning:
"How do they measure cup pressure?"
"Every reloading manual is different how is measured what do they use. Just trying to understand".
With a focus on here in the US and only here in the US SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) recognizes two pressure measuring systems and only two systems.
COPPER CRUSHER SYSTEM
This system employs a copper crusher cylinder that is compressed by a piston fitted to a piston hole into the chamber of the test barrel. The pressure developed by the gases from the burning propellant acts through the piston hole, allowing the gases to force the piston upward, and thereby permanently compressing the copper crusher cylinder. The Sporting Arms and Ammunition Manufacturers' Institute has adopted the pressure units designation of "Copper Units of Pressure" (abbreviated CUP) for this system. This designation applies only to values obtained using the particular crushers, tarage tables and methods outlined in this Standard.
PIEZOELECTRIC TRANSDUCER SYSTEM
This system employs a piezoelectric transducer flush mounted in the chamber of the test barrel. Pressure developed by the gases from the burning propellant exerts force on the transducer through the cartridge case wall causing the transducer to deflect, creating a measurable electric charge. This electrical charge is converted into a reading of pressure. The Sporting Arms and Ammunition Manufacturers' Institute has adopted the pressure units designation of "pounds per square inch" (abbreviated psi) for this system. This designation applies to values obtained with transducers and methods as outlined in this Standard.
The supporting documentation for all of the above can be found in
ANSI/SAAMI Z299.4 – 2015. It is worth noting that the referenced document only applies to Pressure and Velocity of Centerfire Rifle Ammunition for the Use of Commercial Manufacturers. There are similar documents and voluntary standards for shotgun and handgun ammunition.
Purpose and Data:
ANSI/SAAMI – Z299.1 – Rimfire – 2018
ANSI/SAAMI Z299.2 – Shotshell – 2015
ANSI/SAAMI Z299.3 – Centerfire Pistol & Revolver – 2015
ANSI/SAAMI Z299.4 – Centerfire Rifle – 2015
ANSI/SAAMI Z299.5 – Abusive Mishandling – 2016
The matter of importance as far as CUP and PSI are how the test are performed which are identified in the procedures and methods for doing each test. Each method will yield different test results. The numbers will not be the same simply because the methodology used to obtain the results are different.
Something else which is noteworthy is:
"The designation “Copper Units of Pressure” (“CUP”) was adopted by the Technical Committee at their meeting of January 8, 1969, to replace the previous designation of “pounds per square inch.” Advances in the art of pressure-sensing devices had shown that pressures recorded by deformation of copper crusher cylinders are not necessarily a true measure of pounds per square inch for the transient phenomena encountered in sporting arms ammunition".
Prior to 1969 measurements using the CUP methods were frequently reflected as PSI. When newer and better test methods were developed the new results were found to be more accurate and reflected numbers more inline with what actual or true chamber pressures actually were.
That is about it as to how pressures are measured and determined in the US using two different methods.
Ron
