[Unclenick]

The SAAMI system depends on the cross-calibration of pressures and velocities between manufacturers based on their reference ammunition method. SAAMI reference ammunition is made by a manufacturer assigned to the cartridge in question. A lot of ammunition is produced by that assignee with no particular pressure or velocity values except that they fall within the normal range. To establish it as a reference lot, samples are sent to various industry SAAMI members who have pressure guns and SAAMI standard pressure and velocity barrels for the cartridge in question. Copper crushers use copper slugs calibrated by tarage tables and transducers are calibrated hydraulically as described in the SAAMI standard. The participating facilities all equilibrate their guns and ammunition sample to standard temperature conditions and then fire ten rounds, handling each one by SAAMI's prescribed method to keep powder back over the flash hole.

The measurement results from the above are provided by the participating facilities on a standard reporting form. Unless a set of readings is too far different from those achieved by the other test facilities, it and all the readings from other participating facilities are averaged and the average results are declared to be the characteristic peak pressure and velocity produced by that lot of reference loads in a SAAMI standard pressure and velocity barrel. The lot is rechecked this way every two years to compensate for the effects of aging until the lot is consumed and a new lot has to be made.

The maximum pressure listed by SAAMI is called the Maximum Average Pressure (MAP) and the name refers to the average peak pressure measured, and not to the average pressure as the bullet travels down the whole length of the barrel. When a test is done of some lot of ammunition or a test loading, the gun and ammunition under test and a sample of reference ammunition are equalized within a specific temperature range that is not quite as stringent as is used for evaluating reference loads. Ten rounds of reference ammunition are fired, and the resulting average pressure and velocity readings are divided into the pressure and velocity the reference ammo has been established to produce by the multiple facility testing. This results in a relative correction factor which is multiplied by all the subsequent readings taken from that test setup for any lot of ammunition or load samples being tested during that session. This is how the industry calibrates pressure readings to match what the other manufacturers would get.

So, for example, if you could get your hands on some current reference ammunition and you got it and some ammunition you were testing into the right temperature range, and you measured 10 shots of the reference ammunition on your Pressure Trace to average, say, 9,500 psi, but the lot said the pressure average was 10,200 psi by transducer, you would divide 10,200 by 9,500 and the result would be 1.07, and you would then multiply all your subsequent pressure readings by 1.07 to get industry standard psi. If the lot had a copper crusher rating of, say 11,900 CUP, you could also divide that by your 9,500 psi reading to get 1.25 and you could multiply all your Pressure Trace readings by that number to estimate what the copper crusher average would be, and this is probably the only way to get some idea how your load is comparing to old pressure readings done by copper crusher.

The only other detail is that SAAMI pressures are chosen by industry consensus. It is conceivable they have changed as guns have aged. Give SAAMI a call and ask if the first and oldest standard they had (from the 1930s) for the 44-40 can be looked up in their archives or if they know it to be the same as it always was.