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

5K views 67 replies 15 participants last post by  Bryan Austin 
#1 ·
First things first:

1: Any attempt to duplicate / simulate, actual or otherwise, is at own risk.
2: I firmly believe this device is in compliance with ATF "can own it, can build it" guidelines.
3: I have no illusion that results are definitive.
4: Laugh with me, I have no metal working knowledge or tools :)

Now the "Why?"

I got into 10mm a couple of years ago, and being a reloader...

Have all the usual published sources, and initially stayed there. Started playing with QL, and discovered McNett's data.

Very carefully ventured off book, worked up loads with powders there was no data for, measuring everything measurable along the way. 44 powders, 9 primers, 79 different bullets, and 811 loads later, everything is intact. The G20 looks and works as new, and the worst offence is a slightly smiled case (AF barrel, 20# spring, 200 XPT @ 1,275).

That said, from early on I've wanted to know psi.

I've read enough, it's not as simple as a universal chamber from HS, and a piezo from PCB (capital setup. Regardless of equipment, nobody knows what the actual pressures are).

PT II, the only economical, "don't need an engineering degree" option available.

Challenge is, a strain gauge requires a round chamber. Try finding that in 10mm.

The Contender is an option, but $. You can buy an AERO barrel...

Chose a LW barrel (my FIL owns a mill and lathe, and graciously showed me how to turn the chamber to round).

18 months of conceptualizing, a year since I purchased the PT II, and this is what I came up with:

Through the many mental incarnations, I ended up with a metal base, mounted to heavy drawer guides, bolted to a second wood base that would be "field mounted' to a table.



I certainly could have continued used my FIL's lathe and mill, but the 5 hour round trip simply didn't work. To secure the barrel I used an inexpensive barrel vice. Machine work would be rudimentary: An old Harbor Freight hobby drill press; Cordless drill; A few taps; A square.



The aluminum stock was as purchased from a local hardware store's 'scrap' pile, absolutely overpaid for it.

The metal plate glides on heavy duty drawer guides that are bolted to the wood platform. The springs handle recoil. No idea if it'd work, a complete guess.



Mocked up.



Drilling / tapping the thrust block / breech face.



Doing my best to transfer thrust block holes to the metal base.



Thrust block / breech face drilled & tapped. Pictured is the 1st version of the firing pin assembly. The spring creates tension as the pin (threaded rod) is drawn back, the two nuts against the block control the pin's strike depth.



Barrel in vise, chambered dummy round against breech face.



Barrel loose in vise, drawn away from breech face, exposing firing pin. The firing pin (or striker) is a threaded rod, turned down (for the section that passes through the thrust block) by mounting in the drill press and wrapping with sandpaper.



To chamber a round, the vise must be loosened and the barrel drawn towards the front. Insert a round, slide the barrel up to the breech face, tighten the vise.

Not wanting any adventure, I needed a "safety".

The nut pictured pulls the firing pin (striker) out of contact from the primer. The round can be chambered, the vise secured, and the firing pin drawn back to "loaded" all with no danger of a primer strike.





To be "compliant", the device needed a "grip". Searching the garage I found inspiration :)





2nd version of the fire control.



Initial testing (proof of concept) was done at distance with a pull string (Was't going to risk a $30 strain gauge without knowing if it worked!). "Use" trigger will be as simple as a length of fishing line routed from the release through a hole in the wood platform to the grip. The "trigger" will consist of a large key ring tied to the fishing line - Grip the "grip", finger in the key ring, pull!

I'm considering a momentary switch on the grip, triggering a solenoid to release the pin. Neat, but a complication that's not necessary.

Before firing while holding the grip, a safety shield will be mounted to the rear of the wood platform.



In action, tested today, 2/11.

http://10mm-reloaded.com/Pressure_Trace_II_platform/platform.mp4

Tomorrow I'll glue on the strain gauge :)
 
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#4 ·
Thanks guys :)

Yes, my fab skills and tools are, well, crude :)

Literally: A HF drill press with so much run out that I thought the drill bits were bent; A HF rotary tool (works well, I'm surprised); Cordless drill; Jig saw; Sandpaper.

By the time I got towards the end it was "what do I have in the garage that'll work" :)





Today I'll attach the strain gauge and finalize a methodology for calibration.

Not likely I'll secure proof loads, I'll have to use a wide range of book loads, comparing a good size sample of reported pressures with my own results.

Again, I have no illusion that my results will be gospel, but carefully calibrated I believe the numbers will be useful.

And the setup should easily be converted to other calibers.

At very least this project has sparked my imagination a bit, and drained my wallet of $1,250 :)

Potential #'s as early as next weekend.
 
#5 ·
Nicely done. I've been contemplating a pressure trace system but would probably just have a 10mm bbl made for my TC. Mostly as a learning tool plus something to confirm some some theories of mine.
 
#11 ·
Well done. Bravo.
Stay safe and enjoy gathering data!
 
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#13 ·
As much as I'd like to start calibrating, the weather is absolute crap. I have an easy-up, but heavy driving rain is, well, heavy driving rain. It's been a long winter, and it's not even March yet!

Any results being compared to published data will never be apples-to-apples, but I believe I can get close (should everything work).

I came up with the following format, and welcome suggestions.

http://10mm-reloaded.com/load_data/supplemental/Pressure_Trace_II_comparison.html

Now, if the bleemin' weather would clear up for 2 hours!

Loving life in the PNW :)
 
#15 ·
It has been a heck of a winter.

I am frickin' thrilled it is just raining! ;)

Can't wait to start seeing results. Thanks again for setting up this thread.
Isn't that the truth! Just last week I was finally able to liberate the Christmas statues and stuff from my front yard. Classy!
 
#17 ·
Finally decent enough weather to try this contraption out :)

It was a quick trip, and everything functioned as expected.

Since I don't have proof loads, I put together five published recipes with the hope of getting in the ballpark of published #s.

Example:

Published: 155 XTP; Win brass; 6.5gr Universal; 1.260; WLP; 5"; 22.6K
Mine: 155 XTP; Starline; 6.5gr Universal; 1.260; WLP; 4.6"

Challenge - There's enough variables in comparing handloads to published without differing components, yet, for now, those additional variables exist.

Ten shots with the above load proved very consistent results, albeit low at an average of 16.3K.

Underwood's 200gr JHP's trace was chopped (flat top), and only produced 19.4K (Per Recreational Software, chopped traces could mean barrel swelling).

155 XTP / 8.9gr Autocomp (published 35.7K) tested at 24K.

Given that 4 of my 6 working brain cells fell asleep about an hour ago, thought process is / things to consider:

1: Per Recreational Software (RS): All things being equal, results will often be well below published numbers (due to publisher using worst case scenario (tightest chamber, etc).
2: Barrel is brand new (3 shots fired prior to today), and likely could benefit from a few boxes of hot rounds to settle in dimensions (see chopped trace reference above).
3: Dimensions entered into the software are critical, chamber ID being a challenge without the proper tool, which I don't own (used my digital calipers). I've ordered a casting kit, will have the proper measurement by next outing.
4: Too tired to figure out what #4 is...

I'm pleased with the initial results, but frustrated at the same time. Didn't help that I couldn't read the laptop screen (left the easy-up at home), the Sheriff wasn't too pleased my Discovery Pass (use-the-forest-tax) wan't with me, and 10 other people stopped to use the spot I was at.

I'm confident that, with a couple more outings, I can get things dialed in. Only question I can't answer right now (driving me nuts, just the way I'm wired) is: Once everything is working to the best of my ability, and I'm still getting lower than published #s, do I accept RS's explanation (Industry publishers using "worst case scenario"), or do I "correct" the software to show what's published?

Guess the only way to know is to send one of my loads, and my chamber, to a professional lab. = lol $.

Thoughts?
 
#19 ·
Great follow-up. Interesting tof think through this. From the tone of your post, I'm getting a slight sense of, "OK, I have some data, but what did I learn, and what does it really mean."

Very cool project.
 
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#20 ·
From the tone of your post, I'm getting a slight sense of, "OK, I have some data, but what did I learn, and what does it really mean."

Very cool project.
And that's just it, you kinda hit the nail on the head.

For whatever wallet-draining reason, I decided to test an absurd amount of 10mm loads; had (having) a great time doing it! :)

Wanted to add to the information set, a definitive validation of safe vs. "stupid" (at least according to SAAMI). Two years into this project and I'm still having fun, but realized what I've known all along, there's no universal hard stop.

I'm confident there's useful information that'll come from this, or at least amusement :)

1: Work up your loads, understand when to stop.
2: See #1
 
#21 ·
Interesting challenge, thanks for sharing.

I am pretty sure the ballisticans who test for the powder and bullet guys aren't trying for worst case as much as they are trying very hard to match the nominal specs of the cartridge as per SAAMI, so the test barrel is nominal SAAMI dimensions, the cartridge, the bullet, etc.

I think it might appear worst case as most dimension deviations are going to tend to work in the reduced pressure/reduced velocity direction.

You probably will have to send some "proof rounds" to a lab to get benchmarked results if you want precise calibration. Slugging the bore and knowing how close to nominal SAAMI would be good knowledge.

One thing I might try is give Hodgdon, Alliant, Hornaday, etc. a call and ask to speak to their chief ballistician. Maybe send an email of introduction and explanation before the call with the hopes of getting a little advice on variables and how they affect results. They will likely have it on the tip of their tongue.

Good luck, I am definitely pulling for you.
 
#22 ·
Willy

Worst-case is poor wording on my part, should have been stated more along the lines of "highest likely pressure".

I imagine ballistic labs lean towards the "tighter side" of specs - chamber measurements, case wall thickness, primer pressure, powder lot #, etc...

Not to would only invite liability.

Conundrum: Accept results as is, or calibrate to "published"?

Regardless, I may heed your advice. Hear the guys Sierra are good people :)
 
#25 ·
Willy

Worst-case is poor wording on my part, should have been stated more along the lines of "highest likely pressure".

I imagine ballistic labs lean towards the "tighter side" of specs - chamber measurements, case wall thickness, primer pressure, powder lot #, etc...

Not to would only invite liability.

Conundrum: Accept results as is, or calibrate to "published"?

Regardless, I may heed your advice. Hear the guys Sierra are good people :)
I never thought about it, but you are likely right about how they set up the test suites. I have to go back amd look at some of their drawings, but as I recall on a few calibers I have looked at, the tolerances called out in barrel and chamber dimensions are plus x thousandths minus zero on the SAAMI drawings. If that is a standard practice, likely they would use the number called out with no "plus anything". Probably also why I so rarely get what the published velocity was in my results. :)

Also maybe why results vary so much book to book, not just a "good day, bad day" kind of things. I am also starting to get why guns are designed to withstand pressures far in excess of "proof".

Some fun. :)
 
#23 ·
Are you testing on that camping table? That table moved a lot in your video. I'd try something solid like concrete and c-clamps.

Also, here is an Excel file with extensive formulas that lets you calculate barrel pressure based on bore diameter, projectile weight, velocity and barrel length:

http://closefocusresearch.com/downloads/Calculating_Barrel_Pressure_and_Projectile_Velocity.xls

This might be a better and more consistent reference than the claimed data from factory ammo.
 
#28 ·
Cross posted this over at 10mm-firearms:

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
 
#29 ·
Jim at RSI's response:

"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
 
#33 ·
For historical purposes, should anyone decide to go down this road themselves.

I asked Jim (RSI) if 1.25" (barrel OD at chamber) was the minimum for functionality.

His response was:

"No Minimum. Has to do with 8 bit processors and how many steps
are available when converting analog data to digital data.
"

I'm furthering my conversation with him, and we'll know soon enough if the 'math' work-around for my thin barrel suffices or a new one is necessary.
 
#35 ·
I'm fried, but I believe real progress was made 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 :)
 
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