Well, at least you are getting some data.  What was the powder and charge weight?

Quote from: The_Shadow on May 26 2017 09:03:38 PM MDT
Well, at least you are getting some data.  What was the powder and charge weight?

A published load that stated 35K.

Other than lot numbers, my components are identical, save the case - don't have access to new Remington or Winchester.

RSI suggested that case hardness (we know Starline is soft) can have a significant impact on results, hence using a variable (Jagemann).

My chamber is not the labs, and my conditions are not theirs, but a 7 or 8K difference?

Bramwell and Oehler proved the strain gauge accurate, but without a second chamber I won't publish results. Either my setup is in error, or the manu's are padding the crap out of their numbers (I'm not suggesting this).

Ultimately, a ballistics testing lab will be contracted.

This will take months, if not years

Quote from: Benchrst on May 26 2017 08:27:58 PM MDTResults? I'm working on those

I'm thrilled seeing any continued progress no matter how long it takes and thank you for sharing!

Quote from: Benchrst on May 26 2017 08:53:15 PM MDTI've considered that including multiple chambers to the testing will only complicate results, even it they're similar, but it will be part of the process.

Maybe, but regardless I still think there's a chance of benefit in the case there may be some noteworthy information to gain from testing with different barrel lengths.  And then again maybe not.  I do feel it is worth looking into at least.

Quote from: Benchrst on May 26 2017 09:34:35 PM MDTEither my setup is in error, or the manu's are padding the crap out of their numbers (I'm not suggesting this).

I can think of reasons for and against the manufacturers padding their numbers and who knows what else. 

The question I have is;  Do the manufacturers numbers agree with each other's?  To test that numbers would be needed from more than one manu of the same load which are probably few and far between. 

Maybe one bullet manu and one powder manu, not affiliated with each other in any way, tested the same load that they both listed a pressure for?  And then they probably still wouldn't agree with the possibility of different test barrel chambers and overall conditions?

I guess it probably will take an unbiased ballistics testing lab to iron out a correction factor to set up you equipment to, and make your different barrels agree with each other.

However it comes together, keep up the AWESOME WORK!

It is likely a calibration that is going to be need to yield the results from this type of system using a strain gauge.  The RSI Trace system is providing some data with pressures being what they are.
1884  Diff between Hi-Lo
982    Diff between Hi-Lo   This was the best for test for Generic load #1     
2210  Diff between Hi-Lo
The total diff generic Load #1 was 2514 over all three test

935    Diff between Hi-Lo
128    Diff between Hi-Lo This was the best for test for Generic load #2
2343  Diff between Hi-Lo
The total diff generic Load #2 was 3885 over all three test

Glad to see the RSI system producing samples with tight numbers for some of the testing.  With some fine tuning you are likely to see better results and data. 
Thanks for sharing your work in progress...

QuoteSAAMI recognizes two pressure-measuring systems. The preferred system is the piezoelectric transducer system with the transducer flush-mounted in the chamber of the test barrel. Pressure developed by the burning propellant exerts force on the transducer through the cartridge case wall causing the transducer to deflect, creating a measurable electric charge. Pressures measured with this system are expressed in units of "pounds per square inch" (abbreviated psi).

The second, older system employs a copper crusher cylinder which is compressed by a piston fitted to a piston hole into the chamber of the test barrel. Pressure generated by the burning propellant acts on the base of the piston forcing the piston to move, thereby permanently compressing the copper cylinder. Pressures measured by this system are expressed in "Copper Units of Pressure" (abbreviated as "CUP").

Random thoughts and hypotheticals, in no particular order...


A 35K 'recipie' tests at 30K in my rig, 32K at lab A, and 34.5K in lab B. What does that tell us?

What is the possible pressure swing between differing chambers using identical cartridges? Is 8K even possible?

With slow burning rifle powders we know that jamming can have a significant effect on pressure, does that apply to fast burning powders?

I'll load a batch, splitting it into 'standard oal' and 'touching the lands' and post the results.

It would be simple enough to test the hottest boutique ammo, set a global PSI correction within the trace software raising the reading to max, and call it a day. All subsequent testing would 'corrected'. But, is it reality for THAT chamber?

Know that: The PT II records an 'event', and plots a trace according to the parameters entered into the program. Any 'event' can be opened with the software and traced with new parameters (PSI correction, barrel dimensions, brass dimensions), producing a new result. IE, there's always the option of entering a correction later.

The Green Mountain barrel  offers opportunity: 1 blank cut into multiple lengths, cut with the same reamer (heck, could even ream both ends of the same section). The ability to test two barrels
that are 'identical' would validate strain gauges / installation. I've considered what would be gained by having two strain gauges installed over the same chamber.

Blowing a primer = about 2K reduction in reading

Cyanoacrylate adhesives have a shelf life. The first two gauge installations (LW barrel) used glue supplied by RSI. The Kaw Valley installation used approved Loctite 401. I've read that anything less than a perfect bond will yield lower-than-reality pressures. How fresh was the Loctite?

More glue from RSI has been ordered.

So, I'll continue, organize the data best I can, and we can figure out what it all means

I think a key to arriving at the most accurate results between various comparisons will be starting with as consistent a load as possible.  That begs the question;  What load recipe to use geared toward really tight consistency?  I would think the same type of load would be best to use as a verification load over time too.

Quote from: REDLINE on May 28 2017 07:58:06 AM MDT
I think a key to arriving at the most accurate results between various comparisons will be starting with as consistent a load as possible.  That begs the question;  What load recipe to use geared toward really tight consistency?  I would think the same type of load would be best to use as a verification load over time too.

Just some random thoughts on this...

Powders too fast or too slow might make this a bit fussy.... If it were me, I'd use Power Pistol, as it is the most consistent and lenient pistol powder I've used across a wide range of bullet weights.

Bullet weight.... I'd go middle of the road there too...180 grains.

A match primer...I prefer CCI.

Full on match prepped brass.... Sorted for weight, measured for capacity, flash hole centered and checked, trimmed to length so the crimp will be repeatable, etc.

Remove every variable that is within reach.

And to answer a related question that was asked earlier.

Is an 8,000 psi swing from the same chamber/load possible? I'd say yes, I believe the variation in some brands of brass could do that.

For the sake of discussion.... Call it 13.5 grains of usable case capacity (from Nosler 200 grain load data)... That is 13.5 grains of water.

10% of 13.5 is 1.35, and 1.35 grains of water is a VERY small amount.... The point is, it doesn't take much to create a significant difference in case capacity that will swing pressure back and forth by several thousand psi.

I'm gonna run some QuickLoad projections to illustrate this.... I'll post them in a few minutes...I need to measure the chamber of the new barrel anyway.

Yeah.... Just messing around with QuickLoad and changing the case capacity by 1.3 grains I'm getting 5,000 psi pressure swings.

Checking my Starline brass....I get capacity differences as much as 2 grains from within the same lot of brass.

So, there is an easy several thousand psi variable...

QuickLoad isn't an exact science, especially with straight wall rounds... But it can do some useful calculations.

Thanks for contributing Ridgerunner!

I have QuickLOAD as well, might prove useful in all of this.

This project is a bit like the show Lost, every time a question is asked it's answered by three more questions

To reduce the possibility of a strain gauge / attachment issue:

Apparently I do have Winchester brass

Fred Meyer? I might have forgotten.  You live in the PNW?