benchrst builds a Pressure Trace II 10mm platform (PIC heavy)

[sqlbullet]

Might be worth a chamber casting to see how close to SAAMI minimum it is.

[Benchrst]

Might be worth a chamber casting to see how close to SAAMI minimum it is.

Funny you should mention that! I have a # of cerrosafe, and have cast the chamber.

Guess I should head over to the SAAMI site

[PCFlorida]

I too must be late to the party, I missed this one. Great job, please keep on posting about it. Really fascinating.

[REDLINE]

My test 'chamber' is a LW barrel...

4.6"?

[Benchrst]

My test 'chamber' is a LW barrel...

4.6"?

Yes, stock length.

[Benchrst]

Removed the strain gauge, "seasoned" the barrel with a few spicy loads, and attached a new gauge. Tested today, regardless of the load all traces flat-top at 20K psi. Sent everything over to RSI, have a suspicion that it has to do with my barrel chamber walls, specifically how thin they are.

If that's what comes back from RSI I have a plan B

[The_Shadow]

I have wondered if an actual piezoelectric pressure sensor could be mounted.  There was a video of a Beretta 92 which was modified to accommodate the sensor and still cycle the gun.  They had welded bushing to the barrel to hold the sensor.

[Benchrst]

From Jim at RSI

"The problem is that a 10mm barrel is so thin it exceeds the normal
design parameters of the system.  It is designed so with a normal
bolt action rifle and 1.25" O.D./.308 dia chamber, anything that
exceeds safe pressures will flat line.  There is a workaround.


The above spread sheet provides instructions for manipulating the data
so things fall into a normal range.  The numbers are already entered
for your barrel so start with step 3.

Once microstrains have been captured and saved to file they cannot be
changed but after you alter the dimensions to fool the system into
having enough range for the thin barrel, the system will no longer flat
line.  Microstrain values will no longer be valid."


A public thanks to Jim at RSI for getting back to me so quickly!

I'm going to try Jim's suggesting, perhaps as early as this weekend. If it works, fantastic. Otherwise I'll get an ASR pistol barrel or buy a .40 blank and have it reamed.

I believe the end result of this project will be success

[Benchrst]

Progress today

Jim at RSI has been very helpful, and after entering in correcting #s that would allow the system to 'cope' with my thin-walled barrel I tested two loads.

155 XTP 9.8gr 800X trace:



200 XTP 7.8gr 800X trace:



Hodgdon's results for these two loads:



I have no expectation that my #s will match Hodgdon's, but a consistent "close" over a wide variety of loads would help to validate the system.

The trace is still flat topping, and I've reached out to Jim to get his continued input.

The cut-down LW barrel may or may not have to be abandoned - regardless, two additional barrels will be used, each one to validate the other's readings.

I ordered a Kaw Valley AR barrel, it's chamber's walls are significant in comparison to the LW. I should have it in about a week.

Green Mountain's run of .40 blanks will be complete by the end of the month, so with delivery and reaming it's likely 60 days out.

I feel good about this system eventually providing useful and accurate information

[The_Shadow]

Glad you have seen some results and getting to work with the system despite the shortcomings...

[sqlbullet]

This is awesome.  If there werent a wedding I was on the hook to fund in a few months I would be duplicating your system.

After you have it calibrated, I would love to see some graphs from some of the Buffalo Bore and Underwood offerings.

[Benchrst]

This is awesome.  If there werent a wedding I was on the hook to fund in a few months I would be duplicating your system.

After you have it calibrated, I would love to see some graphs from some of the Buffalo Bore and Underwood offerings.

Trust me, I'm quite curious

[REDLINE]

Progress today

I tested two loads.

155 XTP 9.8gr 800X trace:
200 XTP 7.8gr 800X trace:

Looking good.  Did you get velocities too?

I ordered a Kaw Valley AR barrel, it's chamber's walls are significant in comparison to the LW. I should have it in about a week.

Green Mountain's run of .40 blanks will be complete by the end of the month, so with delivery and reaming it's likely 60 days out.

I feel good about this system eventually providing useful and accurate information

What will be the lengths of the two new barrels?

[Benchrst]

Looking good.  Did you get velocities too?

I didn't. As soon as the system is delivering consistent results I'll add a chrono to the mix.

I ordered a Kaw Valley AR barrel, it's chamber's walls are significant in comparison to the LW. I should have it in about a week.

Green Mountain's run of .40 blanks will be complete by the end of the month, so with delivery and reaming it's likely 60 days out.

I feel good about this system eventually providing useful and accurate information

What will be the lengths of the two new barrels?

The Kaw is 4.5", the Green Mountain will likely end up a 6" and a 10", since it ships as a 22" blank.

[REDLINE]

The Kaw is 4.5", the Green Mountain will likely end up a 6" and a 10", since it ships as a 22" blank.

These 3 barrels will all have a strain gage mounted and be used for pressure testing?  That's what I was thinking you were getting at when you mentioned them earlier but I am wondering if it is possible to mount a strain gage to the Kaw barrel if it is this one; https://www.kawvalleyprecision.com/Kaw-Valley-Precision-4-5-10MM-4150-QPQ-AR-15-Barr-p/kvp-10mm-bbl-4.htm

I couldn't find the Green Mountain barrel you mentioned.
I found their website, assuming this is it; http://www.gmriflebarrel.com/
Can you provide a link to the specific barrel blank they offer that you're interested in?