SAAMI maximum chamber pressure for specific cartridges.
| Cartridge | CUPS | PSI |
| 380 Auto | 17,000 | 21,500 |
| 9mm Luger | 33,000 | 35,000 |
| 9mm Luger +P | 38,500 | |
| 38 Special | 17,000 | 17,000 |
| 38 Special +P | 20,000 | 20,000 |
| 357 Magnum | 45,000 | 35,000 |
| 40 S&W | 35,000 | |
| 10mm Auto | 37,500 | |
| 41 Mag | 40,000 | 36,000 |
| 44 S&W | 14,000 | 15,500 |
| 44 Magnum | 40,000 | 36,000 |
| 45 Auto | 18,000 | 21,000 |
| 45 Auto +P | 23,000 | |
| 45 Colt See Special | 14,000 | 14,000 |
| 45 Colt +P | Not Defined | Not Defined |
Notes:
SAAMI ( Sporting Arms and Ammunition Manufacturing Institute) is an organization that defines extensive definitions for cartridges of ammunition. It includes the cartridge physical dimensions as well as maximum chamber pressure. This ensures that ammunition manufactured as a specific caliber is safe for that type of firearms with assuming a firearm in a good functioning condition.
Copper Unit of Pressure (CUP) is a measurement used in the ammunition industry to determine the chamber pressure created by a cartridge load. Originally, a precisely formed copper slug was placed in a fixture over the chamber. When the cartridge was fired, the amount of crushing measured on the slug allowed engineers to determine the pressure.
These days, modern electronic transducers provide faster, more accurate measurements of chamber pressures in pounds per square inch (PSI). CUP and PSI are measured to different scales and are NOT interchangeable.
+P Ammunition — This ammunition is loaded to higher pressures than the original level of that caliber. It is typically used for defensive ammunition. It’s overall size and shape is identical to its parent cartridge, so care should be used to only use +P with firearms with sufficient strength to handle the additional pressure.