I believe the other one is CUP, rather than CIP. They refer to two different methods of measuring pressure, rather than two different specs. Because of the differences in the two methods of measuring the pressure of a fired round, you get a significant difference in the pressure reading for the exact same load. Theoretically, neither is better or more valid than the other, they are just different, so you need to know which method was used to get the pressure reading to keep from comparing apples and oranges. CUP is by far the older method, and the units of the reading are Copper Units of Pressure; the pressure barrel actually has hole in it into which is inserted a copper pellet which is then crushed by the ignition of the cartridge, and the "pressure" determined by mearurement of the deformation of the copper pellet. The SAAMI psi spec is based on a pressure measurement taken from a specialized single use load cell (at least it was single use when I first encountered the method; that may since have changed) incorporated into the cartridge case or test barrel (can't remember which) and is a much newer method of determining pressure. While I said that theoretically they are about equal in accuracy, the SAAMI method is generally considered to be more precise, with good reason, given the capabilities of modern load cells. The main thing to remember is that you are using two different pressure scales and measurement processes, and you can't really convert from one to the other reliably. If you are interested in precision of pressure measurement, assuming the skill of the testors is equal, the SAAMI method is the more precise of the two by the nature of the process used to instrument and record the measurement, but this doesn't invalidate the much older CUP method, it just offers a more modern, more exacting alternative. As long as you don't compare pressures from one method directly with measurements from the other method, you'll be fine no matter rating you use. A maximum pressure for CUP is established for each load tested by that method (mostly that's test data that has existed for years), and a maximum PSI for each load tested by the SAAMI method is established for loads tested using that method. As long as you compare a CUP pressure rating to the CUP max load rating and a SAAMI PSI rating to the maximum SAAMI psi for that load, you're fine. Since the actual number for CUP is a good deal lower than a similar SAAMI PSI rating for the same load, comparing a CUP test result to the SAAMI max load PSI rating will definitely yield a false sense of security. Again, as mentioned above, stick to apples to apples comparisons and oranges to oranges comparisons and you'll be fine. Just don't mix the two. And remember that data expressed as SAMMI PSI units usually represents more recent data determined with a test protocal that is (mainly due to improved test instrumentation components) more precise. But with many loads, old CUP data is all that exists, since there is no need to reinvent the wheel (pressure testing equipment and testing protocals aren't exactly cheap) just to express a test result in a new rating scale, and unless some outfit already has a test run scheduled with it for, say, the introduction of a new VLD bullet, why go to the expense of testing a 30-06 with a 170 grain bullet and 4064 again when that combination was tested to death with a copper crusher test barrel 40 years ago? Like so many things in our lives involving engineering, the data that exists is often driven by economics as much as snything else....
