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

[Benchrst]

Cross posted over at GT.

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 will be 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 yesterday, 2/11.

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

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.

[The_Shadow]

Very cool  , I commend you and your efforts!  Carry on! 

[Benchrst]

Thanks Shawdow!

If the weather cooperates I'll be calibrating next weekend!

All gussied up



The other half of the operation.

[Ridgerunner665]

Count me in as another one who is following this with great interest.

[sqlbullet]

Really cool.

Amazing what you can build with a drill and ingenuity.

[Benchrst]

(Cross posted over at GT)

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?
?

[The_Shadow]

That is what I have tried to understand with that system all along...you need to adjust the input to get results of output.
This system is based on the stretch of the strain gauge that is wrapped around the barrel surface.

This might can help you do a comparison to dial in the data...


Good luck getting things sorted out.

[tommac919]

All I can say is WOW !

[Benchrst]

Thanks Shawdow.

Next steps:

Run 50 rounds of nuclear through it, settle in the chamber.
Cast for absolute chamber measurement (curious to compare cast to my inside caliper measurement).
Reset the strain gauge.

Continue to test published loads (Hodgdon lists components used).

If, after the above, results are significantly lower than published numbers I'll enter a correction within the software.

Interested to see if a high pressure load reads near published after correction for a low pressure round.

At least I'm having fun

[REDLINE]

NICE WORK!  Seems I'm late to the party.   Better late than never.   This is exciting stuff!  I've been lusting after one of those Pressure Trace units for many years now.  Just never been able to swing the funding which is probably more attributed to poor money management than anything else.

Is the LW barrel 4.6 inches long like a standard Glock 20 barrel?

...or do I "correct" the software to show what's published?

Thoughts?

My thought would be yes to that.  Though I'll be curious to find out, if after you've corrected for one published load, if any other published load agrees with that correction factor.  Wouldn't surprise me if one powder manufacturer's published data doesn't agree with another's.  But who knows.  Testing should tell within reason.  I suspect you will still have to resort to an educated guess, just a much closer one than if you didn't have any published data to compare with.

I'll be anxiously watching for all future developements as you move forward.  Keep up the great work!  And BTW, nice job on that shooting contraption you built.

[REDLINE]

That is what I have tried to understand with that system all along...you need to adjust the input to get results of output.

Does that leave room for negative issues?

[Benchrst]

Thanks Redline!

Next step is to season the chamber a bit (if the weather EVER breaks), attach a new strain gauge, and resume testing.

I understand the necessity, or rather the needed ability, to make a universal correction for a specific gauge setup - THAT particular gauge, it's unique install, the glue used...

And I agree with your thinking, and it's my intent to make a correction (should it be necessary) and compare against multiple published loads. If the correction puts my results near reported then success. At least in reporting a specific load by published standards.

My components are a close to published as can be, but even if I, Alliant, Sierra, and Hornady tested identical loads, on the same day, at the same altitude, with the same cosmic alignment, we'd get different results.

[REDLINE]

...but even if I, Alliant, Sierra, and Hornady tested identical loads, on the same day, at the same altitude, with the same cosmic alignment, we'd get different results.

I would expect that if you all were using a different system to test pressure.  But I tend to think if you all used a properly set up PTII, calibrated properly (even if not to an identical ammo load), that you would all get relatively close results.  The main variances being altitude and different lots of powder.  The PTII is already figuring in barrel temperature. Just my thought.

[Benchrst]

...but even if I, Alliant, Sierra, and Hornady tested identical loads, on the same day, at the same altitude, with the same cosmic alignment, we'd get different results.

I would expect that if you all were using a different system to test pressure.  But I tend to think if you all used a properly set up PTII, calibrated properly (even if not to an identical ammo load), that you would all get relatively close results.  The main variances being altitude and different lots of powder.  The PTII is already figuring in barrel temperature. Just my thought.

I agree, but chamber dimensions have to be a factor.

My test 'chamber' is a LW barrel turned down to round. I suspect it's on the tighter side, but I really don't know.

Regardless, the weather is supposed to clear for two days in late August 

[REDLINE]

I agree, but chamber dimensions have to be a factor.

My test 'chamber' is a LW barrel turned down to round. I suspect it's on the tighter side, but I really don't know.

Makes sense. Neat that the PTII takes that into account too.

Regardless, the weather is supposed to clear for two days in late August 

LOL