Sources for Pressure Data?

[mikecr]

I didn't mean 'calibrate' as in taken to national primary standards. I meant just what you're doing Clark.
No manual, or test barrel results, or even strain gage testing will get you there(where we really need to be), like tweaking QL with good chrono data & webline measurement with calipers.

Nobody will ever be able to 'lookup' their pressures in a book..

 

[Jay Christopherson]

If anyone wants a RSI Pressure Trace II system (+ strain gauges), I've got one I'll sell you. I don't have the time to play with it as much as I did when I bought it. It's an interesting tool to use if you are looking to validate or verify certain things.

 

[CPorter]

I have read Vaughn so it is entirely possible. I have made several items traceable to NIST and it would be traceble in the range in the range checked.

 

[mikecr]

I'm sure pressure traces could be calibrated and accurate -for determining pressure. And I do believe that seeing what's going on with powder burn is useful. Nothing against pressure measurment from me.
But neither pressure measurement, nor QL, are replacements for the other.
This isn't a Chevy-vs-Ford thing as they are completely different in what they do, and with different objectives all together.

You can't run a pressure trace and determine from it, by itself, that your load is a problem for brass. You'd measure your brass to validate this.
You can't enter values in QL and determine from it, by itself, that a load is a problem for brass.
Again, you'd measure your brass to validate this.
In both cases, that brass measurement feedback is needed to lock in on the local meaning of what you're seeing.

QL doesn't measure anything. You use a chrono and/or pressure trace along with brass measure to calibrate QL. With this you can predict loads and results of them very accurately.
You can't predict anything with pressure trace, it doesn't predict. It measures.
Different purposes all together.

They are both useful, local, and so way beyond data in any book.

 

[Clark]

I didn't mean 'calibrate' as in taken to national primary standards. I meant just what you're doing Clark.
No manual, or test barrel results, or even strain gage testing will get you there(where we really need to be), like tweaking QL with good chrono data & webline measurement with calipers.

Nobody will ever be able to 'lookup' their pressures in a book..

I understand.
My wife and I are engineers, she designs calibrators. Being around her grammar NAZI habits has made me a dull boy.

 

[Clark]

CPorter

I have read Vaughn so it is entirely possible. I have made several items traceable to NIST and it would be traceble in the range in the range checked.

Vaughn does 12k psi and warns not to go to 15kpsi.

I think if chronographs were inaccurate and of unknown error, you might still find some use for them, but the transducer measurements are worthless.

The idea of using a strain gauge to find the threshold of long brass life instead of looking at the brass, must meet some definition of insanity; taking leave of the senses.

All SAAMI registered max average pressures of high pressure cartridges are, in some Rube Goldberg way, simply reflections of the threshold of long brass life. The load books will not tell you that. Not recent ones.

The goal is not to find a load of a certain pressure. The goal is to find the threshold of long brass life and then subtract a safety margin for process error.

Denton Bramwell seems to be able to do math and memorize processes, but needs supervision on staying focused on the goal for a handloader, not a commercial loader.

 

[CPorter]

Strain gages are used in all manner of pressure sensors, do you have something against them or just the attachment method used by the pressure trace?

 

[mikecr]

I think what Clark and I are suggesting is that knowing the pressure, even actual pressure, is of less importance than knowing local max pressure for the component combination at hand.

This is how I determine MY max pressure:
I incrementally raise the charge, measuring at the webline with calipers. As I go up in load, new brass will grow there and settle to expanded chamber diameter minus springback(leaving clearance for easy extraction). As I continue to go up the webline will -step change- at some point another .0005" to .001". This is MY max, because I don't FL size.
It's the point where I typically get a hitch in extraction from brass yield leaving an interference fit, and where body sizing will always be required. With .473 casehead cartridges this is consistently indicated as ~58Kpsi in QL regardless of the load causing it.
A benchmark in a sense, because if this holds as true, QL predictions beyond should be reliable.
SAAMI max is often around 60Kpsi for these cartridges, and I'm sure FL sizing is assumed there for reloading.

Yeah it's anecdotal and there are other factors that can affect this. Other case diameters, amount of barrel steel around the chamber, chamber clearances, etc. But if measured velocities are predicted close by QL, the pressures shown are right enough in my book(so far), and pressures that become an issue are usually still within safe limits.

PRESSURES THAT ARE CAUSING ANY ISSUE..
In my experience, anyone would have to blow by many signs, or push it beyond utterly stupid, before getting into trouble. If there is any issue, stop, that is your MAX, until resolved or understood and accepted.
This is more important than the 'actual' pressure

 

[Clark]

This is more important than the 'actual' pressure

To get through sometimes a joke will help.
Q: "Why can't your denomination make love standing up?"
A: "Because it looks too much like they are dancing."