I agree for the most of us CUP and PSI is like comparing a MIL/MOA scope adjustments. Sometimes it just doesn’t work.

Later, Frank
Bartlein Barrels

I should apologise for any slight implied.

To me though, talking in CUP and comparing it to PSI is like having a Milradian optic whilst thinking in MOA, whilst trying to shoot at long distance. The maths does the head in. (Not a perfect analogy!)

The problem in making any comparison in ‘quality’ load manual data is still not quite so simple, and the unit of measure differences simply complicates an already challenging issue.

We all know that load data is based on certain standards (SAAMI & CIP) as well as manufacturers tolerances. Further, as most would know, the influence of temperature can vary velocity (and therefore obviously pressure as a result) quite widely. I want to know by how much and whether these fluctuations are within safe limits by comparing it to something I can make sense of. It is impossible for any printed load guide to address all the variables, to cover all possible scenarios. Being within the published velocity bounds can be a bit of a guide, but then …

Load manual data, regardless of unit of measure, is published based on specific standards, as they should be (for temperature, air pressure et al) but these are only sometimes published and I for one shoot in an environment that is way outside some of the standards I know about.

A strain gauge ‘guestimate’ is as you say fraught with some potential error and perhaps not even a ‘standard’ at all, but under the circumstance, better than nothing. Comparing it to CUP data is impossible and pointless. If only PSI is used, that’s at least one issue out of the way. The strain gauge yardstick may be cut from a tree branch, but it should at least be roughly in the ball park. Published load manuals published in CUP using standards the vary from my actuals by more than 60 degrees F, well quite simply, I have no yardstick by which to value such data at all.

To Steve Hurt: Nearly all of the ammunition test barrels we make for Hornady are the Piezo transducer. So they are in the 21st century.

Second it is not necessarily up to the ammo maker/firearms manufacturer which system to use. In some cases the standard for a given caliber might be CUP testing. With that being said we make very few CUP style pressure test barrels anymore but every once in a while we do and usually it’s for a odd ball caliber.

Until the standard is changed for a given caliber it’s the way it is. With that being said also some makers do buy a Piezo style test barrel along with CUP style barrels for testing of the same caliber.

Later, Frank

Why is CUP,LUP,PSI important when the average loader has little if any access to the resources to measure these? Explicitly follow well publicized guidelines based on fire arm and desired effect. In the meantime, put your dick in your pants.

The CUP measurement method is a pretty basic system in modern times, giving only the peak force on the crusher, but then again its simple!

Although I haven’t been working in the ballistic instrumentation and photography field for a few years, copper crusher gauges were still used for large caliber weapons systems when I was there. We are talking artillery and tank guns here. They were mainly used as multiple gauges could be placed within the charge and inside the chamber of the weapon system. Though simple, calibration of the copper slugs or balls crushed in the gauges required a piezo measurement system. The piezo gauges calibrated beforehand using high-pressure (upto 10,000 bar, 145,000 PSI) Budenburg oil and dead weight calibration equipment.

As to personal use of pressure testing equipment, piezo-based systems are simply not cheap, nor is modifying the firearm beforehand. Also the Pressure Trace II system you mention is not a piezo-based system, it uses strain gauge technology. Though useful as a guide, the problem with this measurement method is calibration. For accurate results you need the chamber material properties and dimensions along with the strain gauge properties, in addition the chamber and outer wall temperature. If you don’t do this, the best you’ll get is a pressure guesstimate. Even if you use factory ammunition to calibrate the system before hand, do you know the actual pressure produced by the factory round, unlikely. All you’ll know is that you’re ammunition does not exceed the factory ammunition peak pressure, what that pressure actually is, well we are gussing again.

Neil

1) Much of the SAAMI cartridge spec data is still in CUP.

2) Replacement of copper crusher gauge (CUP) test equipment for piezoelectric based systems may be prohibitively expensive.

CUP-based setups tent to be mechanical only, so do not require any form of computer or electrical supply. Even the measurement of the crushed gauges can be done with a mechanical micrometer.

Anyway, at least its rare to see LUP (lead units of pressure) now. So we don’t have yet another measurement system to worry about!

Being in the UK, I stick with CIP data, which is in Bars, easily converted to MPa or PSI, and testing is undertaken with piezo-based system.