When Lyman did the testing, they used a lead crusher instead of a copper crusher, but probably the same picture to hole the pellets. The modern way would be with a pezio pressure adapter for the barrels or an electronic readout from a sensitive apparatuse attched tot he barrel -maybe that 's the same thing . It measures using strain gauges or something similar and gives direct readouts in pounds per square inch (PSI).
In the crusher system, a hole is bored in the barrel, and non-deformable plunger inside the hole. On top of the plunger is a plug of maleable metal, copper or lead depending on the range of pressures being measured, that is held there by the fixture above, which is also non-compressable. Below about 15,000 copper units of pressure, lead is used instead of copper, for the crusher. Above that level of pressure, copper is used. The shot is fired and the presssure generated pushes the non-deformable plug up against the 'compression plug' and compresses it in length. The resulting plug is measured in length and the difference in length from new to compressed is comparred to a Tarrage table, which gives a # expressed in lead or copper unites of pressure, thus the letters Lyman used as designating pressure in LUP or CUP.
In Europe, they use a similar system, called CIP (not sure waht thos leters mean), but they also call the resulting number, PSI - or pounds per square inch - which it actually isn't. This creates a LOT of confusion amongst the ranks. We know here, that the CIP number is very close to the US system of CUP numbers (similar numbers), and that the newer electronic measuring devices that read out in PSI give numbers very much higher than the numbers given by either CUP, LUP or CIP.
We are told you cannot convert CUP or CIP to real pounds per square inch. That is so, but we also know that straight cased rounds, such as the .45/70, the other Sharps rounds, as well as straight pistol cases when tested on a crusher machine giving CUP numbers, that those numbers are almost identical to electronic PSI generated numbers. What this means, is if the .45-70 or .45/120, .44 magnum or whatever straight case, gives 28,000CUP, that it is actually producing 28,000PSI as well. This co-relation is not generated with bottle necked cases, ie: for example, a .270 producing 55,000CUP, is actually producing 63,500 PSI, not 55,000PSI, while other cases/rounds producing 57,000CUP, are actually making 62,000 or 63,000PSI. There is no cross referencing or formulation that is accurate for comparing these numbers produced by cottle necked cases - they all vary to one degree or another, as most all bottlenecked cases don't produce consistant differences between the PSI and CUP numbers.
Unfortunately, through the 1900's to about 1990, some writers and book writers were expressing CUP numbers for modern rounds as being PSI. Even PO Ackley did this in the .50's. They didn't have the electronic or pezio testers to show them there was a difference and that CUP numbers could not be converted to PSI. This has caused a lot of confusion in relation to actual pressure. We know today that PSI is repeatable, while CUP, due to the mechanical nature and quailtiy of materials used being 'sloppy', produces numbers that are considered inconsistant today. It was OK back then, but this is today.
What does this mumbo-jumbo have to do with us? Our muzzleloading barrels are very similar to straight cased rounds, that's what. This means that CUP or CIP or LUP numbers are close enough to actual PSI to use them interchangably. So- if the readout is 15,000LUP, that load is producing very close to 15,000PSI as well, 8,000LUP is very close to 8,000PSI, etc. The reason for mentioning all this, is to give some meaning to the nomenclature used by industry, etc. Being able to use PSI gives us a base of comparrison - 15,000 PSI is not much, but is considered very close to maximum usable pressure for an open ignition system. Closed systems, and finely tuned systems can absorb more, such as the slug guns, platinum lined nipples, etc. Normal muzzleloading systems burn out with high pressure. Note that Accurate Arms loading manual gives PSI readouts for the Sharps rounds loaded with their powders. They first used GOEX in the appropriate, original-type loads, recorded the pressure, then developed load with their powders to match the pressure of those BP loads. The .50/90 using a 450gr. bullet, 90gr. of powder, produced something like 28,000PSI. The .45/70 BP factory-type load produced 22,000PSI. That was 70gr. of 2F with a 405gr. lead bullet. No wonder the modern black powder slug shooters need special nipples for their rifles. Some have said a regular stanless nipple lasts for only 5 to 10 shots. It's all about the pressure being generated. I shudder a bit when I recall the 120gr. 2f charges I used to shoot in the 15/16" barrel, poorly designed cast breetched TC "Hawken", with 370Maxi's and 450gr. Lyman bullets. No wonder I needed to replace nipples often. It didn't take long before the hammer was being lifted off the nipple to 1/2 cock.
Note in Lyman's book, they loaded to a maximum of around 15,000LUP. Look at the velocity of the ball. Compare that velocity to another calibre, and you will see that the larger or smaller gun produced the same velocity at the same pressure.(the numbers vary slightly, but not much). Note in the .58 cal. gun tested, they used powder charges up to 160gr. or 170gr. of GOX and 180gr. of 3F C&H powder, yet the pressure was still below the 15,000LUP(PSI) used as max in the smaller bores. We know today, that the powders being produced are somewhat stronger than those used when Lyman published the 'book' - BUT - what we also know, is that when the velocity is the same, so is the pressure, ie: a .69, if producing 2,100fps, it is producing the same pressure as a .50 cal rifle producing 2,100fps.
Take a look at their data and find a .45, .50 or ..54 producing 1,200fps and read off the pressure. In a .73 or .75 cal gun, it takes 120gr. of 2f to produce that velocity. This shows the big ones operate at very low pressure.
All kinda interesting - no?
