Pressure signs ?

I really got my money's worth from my PressuretraceII. I know most of you shoot those exotic calibers but for some caliber like the 44-40, the shooter will far surpass the strength of certain firearms, like revolvers vs the post 94 Marlin/Winchester rifles long before the cartridge gives in to high pressure signs.
 
Cdoc42,

None of the formulas work well because they are simple linear regressions. The reason that doesn't work well is the copper crusher output curve has a knee that bends toward flatter as the pressure gets higher, possibly due to gas piston inertia becoming a more significant source of offset error as pressure goes up, while piezo transducers are more linear. There is a graph comparing the two for 30-06 on page 43 of this paper.

Denton Bramwell's formula is just to show there is a degree of correlation in rifle cartridge readings from about 28,000 psi up, but it isn't a tight correlation. Consider that SAAMI CUP for MAP for the 223 Remington and the 308 Winchester and the 270 Winchester are all equal in the copper crusher at 52,000 CUP. But the same reference loads tested in the SAAMI type piezoelectric conformal transducer system give those three cartridges 55,000 psi, 62,000 psi, and 65,000 psi MAPs, respectively. So any formula that converts 52,000 CUP to psi will be no more accurate than that 55,000 to 65,000 psi result. Since 60,000 psi is the average result there, that works out to about ±8% error.
 
Thanks Unclenick. It's somewhat frustrating to see new data in Lyman's 50th manual and on Hodgdon's website where loads have CUP or PSI listed for individual recipes, making comparisons useless when I'm comparing velocities with lowest pressure.
 
It's interesting to compare pressure listed for a given cartridge across all data sources. Same for velocity.
 
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There was once a company that would pressure test your loads in your barrel. Just unscrew it and send it in. Problem was, to do that, they used an axial gauge kind of like the old British system. Therefore the numbers did not agree with anything published in the USA or Europe and you just got a comparison with a standard load. I don't recall whether they used real SAAMI reference ammunition or just a factory load.

Haven't seen anything about them in a long time. Probably obsoleted by strain gauges and Quickload.
 
It's somewhat frustrating to see new data in Lyman's 50th manual and on Hodgdon's website where loads have CUP or PSI listed for individual recipes, making comparisons useless when I'm comparing velocities with lowest pressure.
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I read somewhere in one of my Lyman manuals that they switched to PSI for new testing. And old data is listed with CUP.
The trouble with comparing pressure from CIP and SAAMI is that they sample the pressure at different locations. SAAMI spec is to sample the pressure near the middle of the chamber, between the case head and mouth. CIP takes the measurement after the case mouth. The difference in location changes the pressure that the instrument reads. If you compare the listed max for multiple cartridges from both systems, the CIP numbers are significantly different. But if you test the same lot of ammunition in both systems it will give similarly different numbers, but they will be close to the same percentage of the max for each system. But it is not perfect.
 
Big Al Hunter,

You've got a couple of different European systems conflated. It's the NATO EPVAT protocol that uses gas ports in front of the case mouth for pressure. The CIP uses chamber ports lined up with holes drilled in cases with the same port size and location for their Kistler piezoelectric transducers that they used to use with their copper crushers. That system is called a channel transducer in both instances. The NATO version has the advantage you don't have to drill and align the case hole with a measuring port in the chamber for each shot, and the disadvantages that pressure drop behind the bullet can lower readings roughly a 140 bar (just over two thousand psi) and there are resonances with the transducer due to ringing caused by the abruptness of the pressure exposure. That ringing at around 200 kHz has to be filtered out of readings or a false high number is obtained.

The SAAMI copper crushers use a mid-case ported chamber, but with the hole located around mid-case and is different for different case sizes, while the CIP locates most ports at one of several fixed distances in millimeters from the case head. The SAAMI conformal transducer uses a still different pressure sampling location just below the shoulder of bottleneck rifle cases where no hole is drilled. Instead, the transducer "piston" is shaped to conform to the chamber profile at that place so the pressure is contained in the brass case and measured over top of it. Reference loads are used to adjust for resulting reading errors. You sometimes run into pressure test cases on the once-fired market. They have a distinct ring where the transducer piston was over top of them in the chamber.
 
You've got a couple of different European systems conflated
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That's what happens when I trust my memory. :o It has been a while since I've studied the topic. Your explanation sparked my memory. You are correct, there are that many systems for testing. And each has a max pressure that is different for the same cartridge. It causes a great deal of confusion, especially when you don't know about the different systems.
 
If you read most comments on cartridge pressure too closely,
You could get the impression that you'll be wasting your time!!!
I dis-agree!!!.

For my reloading; measurements, data and notes on the various pressure signs keeps pressure in the forefront of my mind.

I chrony all my reloads. I do look for a velocity drop in the last near max to max loads. I only use the same primer, With a magnifying glass I can see this primer flatting as I work up for min to max pressure (Also can see the difference between max loads from a 7.7x58 to 308 onto a 270W). I also measure the before and after pressure ring diameter, I can easily calculate this difference increase working up from min to max loads.

Not hard to take a chrony, a magnifying glass and a caliber with me with to shoot a these min to max work-ups and check each cartridge as I shoot'em.

When I put all this together,
I have elected to pull and not to shoot the last max load or
elected to stay a step down in future from that last max load.
But most importantly to me, It keeps pressure signs in the forefront!
 
I also measure the before and after pressure ring diameter, I can easily calculate this difference.
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Are all cases of a given cartridge the same metallurgy and wall thickness and shape at the pressure ring plus the same clearance to the chamber wall?

That condition has to be met else the same load will have different pressure ring dimensions after firing across all those variables.
 
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