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MSM2019
PostPosted: Sat Jan 01, 2022 12:46 pm  Reply with quote



Joined: 04 Mar 2019
Posts: 1819
Location: Central ND

Has anyone purchased a strain gauge or a Pressure Trace II system?

If you went the strain gauge route, from what company did you buy the strain gauge and what software are you using?

If you bought a Pressure Trace II, how do you like it?

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Hammer bill
PostPosted: Sat Jan 01, 2022 2:14 pm  Reply with quote



Joined: 09 Feb 2015
Posts: 815

Never herd of neither. Enlighten me sir.
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MSM2019
PostPosted: Sat Jan 01, 2022 3:20 pm  Reply with quote



Joined: 04 Mar 2019
Posts: 1819
Location: Central ND

Background......I have always wanted a piezoelectric transducer system to check shotshell pressures, however the price has gotten to the point where I would have $15,000 plus sitting around collecting dust.

After talking with someone in the industry, it was suggested I look into strain gauge technology. A strain gauge is very thin plastic strip with some type of resistance wire or foil laminated in the plastic. When stretched it changes resistance and gives a different electrical output, which can be hooked into a computer which would have software that converts the electrical reading to PSI. The strain gauge is attached to the shotgun barrel at the chamber radially. When you set off the cartridge the barrel stretches, stretching the strain gauge and then giving you a reading. It is quite a bit cheaper than a piezo system.

The Pressure Trace II is ready to go with the exception of affixing the strain gauge to the barrel and downloading the software. A bit more money, but doable.

Since I am not looking to do research I don't need a pressure gun. Even if the load I was developing exceeds SAAMI, at most it would only be a couple thousand PSI over and that won't hurt a modern, well maintained barrel.

I am not well versed in what company might have strain gauges with a program to read the inputs. Lots of companies make strain gauges for all types of applications. I need a bit of direction.

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skeettx
PostPosted: Sat Jan 01, 2022 3:55 pm  Reply with quote
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https://www.youtube.com/watch?v=uP6Alb6V17U

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MSM2019
PostPosted: Sat Jan 01, 2022 4:03 pm  Reply with quote



Joined: 04 Mar 2019
Posts: 1819
Location: Central ND

Thank you Mike!!

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RGuill96971
PostPosted: Sat Jan 01, 2022 4:09 pm  Reply with quote



Joined: 21 Mar 2019
Posts: 519
Location: Texas

Mark:
About 2 months ago I was ready to pull the trigger on the trace II. The company that makes the pressure trace has all the stuff on their web site. I even called and talked to the owner, he was a really nice guy with lots of info, suggest you give him a call.
Shortly after, I was sending some loads out to Tom to be tested and I brought it up to him. He seemed to imply that without reference ammo the results would be hit or miss at the best. Like you, I wasn’t interested in scientific results, just in the neighborhood for my own knowledge. I don’t get all bent out of shape, if a load for say 12 gauge is 12,000 psi. It was his belief, and the other guy I use (Bruce) to test loads, that if I used a tested load from one of them as reference, I would get within 1000 psi.
I’m sure you know there is a guy over on shotgun world, that uses very often and he says he likes the system and it serves his purpose well. From what I understood if you are careful with the strain gauge when it’s attached you can use it more then once.
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MSM2019
PostPosted: Sat Jan 01, 2022 5:40 pm  Reply with quote



Joined: 04 Mar 2019
Posts: 1819
Location: Central ND

RGuill96971,

You do need to have reference ammo, without it you are just guessing. Even though a shotgun will easily stand a load 2,000 PSI over SAAMI MAP it isn't a great idea. Kinda like driving 100 MPH instead of 70 MPH, just more wear. Or you have a load that is under performing neither is ideal.

Most of the loads I want to play with are hunting loads, so I want to get as close as I can.

I have my own reference load that Tom Armbrust tested a few years ago. I'd really like some SAAMI reference, if I can get my hands on some.

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RGuill96971
PostPosted: Sat Jan 01, 2022 5:55 pm  Reply with quote



Joined: 21 Mar 2019
Posts: 519
Location: Texas

Agree. I don’t see any reason a tested load would not work as reference. I also ask about getting some Saami reference ammo, from what I was told it’s really hard to come by. The guy that tested my last rounds said he waited a year on them.
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Brewster11
PostPosted: Sun Jan 02, 2022 10:26 pm  Reply with quote



Joined: 08 Feb 2009
Posts: 1301
Location: Western WA

Mark,

A strain gauge or the Pressure Trace II is a laudable objective, especially for 16ga reloaders, but when I investigated the options myself, I found the calibration and cost issues to be problematic. A strain gauge might have to be recalibrated each time a new strip is installed. The PTII is great but quite costly.

A CUP test barrel might be a better DIY option. They are simple to fabricate, very low cost, and would require no calibration because it is a direct measurement. The conversion from CUP to PSI is sufficiently straightforward to suit our needs. The slugs were still commercially available a couple years back. However, lacking a spare 16 ga barrel, I eventually shelved my plans. Maybe you might have better luck; it would be nice to have a quick pressure test at little or no cost, as we 16 gaugers have to make do with whatever powders and components we can scare up today.

V/R
B.
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nj gsp
PostPosted: Mon Jan 03, 2022 6:39 am  Reply with quote



Joined: 09 Aug 2007
Posts: 437
Location: WI

Strain gauges are used extensively for bulk storage inventory management on silos, hoppers, bins, etc.

It's nothing more than a sensor that measures expansion and contraction with high precision. Once calibrated with known values (a zero value and a known peak value) the output should be vey repeatable unless the sensor is disturbed.

Recalibration would only need to be done if the strain gauge was removed and reinstalled somewhere else. If the sensor was permanently attached and used on a dedicated firearm, recalibration/verification would not be necessary except on some periodic basis as recommended by the manufacturer.
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MSM2019
PostPosted: Mon Jan 03, 2022 8:01 am  Reply with quote



Joined: 04 Mar 2019
Posts: 1819
Location: Central ND

I use reference ammo almost every time I setup my chronograph. You really have to. Reference ammo is part of testing. The very first thing you do once you have the test rig setup is shoot two warming rounds and then run reference ammo. I have my own reference ammo for both 12 ga and 16 ga lead target and hunting loads. Nothing special just ammo that was tested and you buy enough powder, primers and wads of the same lot number to keep you going for awhile.

SAAMI reference is hard to get if you are not at least an Affiliated Member. An Affiliated Member would probably be someone like Precision Reloading or Tom Armbrust.

When Precision was in CT, we were an Affiliated Member, mostly to get our hands on reference ammo. So for that stuff I might have to ask a favor or two and only use it when I have to.

I have a 16 gauge 870 that would be perfect for this, I would just buy another barrel, ream out the choke and dedicate it to testing only. That way the strain gauge would stay put.

As far as using a lead crusher, I am really kind of against that. Mostly because I really want to explore buffered loads, steel loads and some of the other non-toxic stuff. Those are the loads that sometimes "hid" the pressure spike when using lead crushers. If I was only shooting target and light hunting lead loads I might be open to it. That is about a $5000 investment between receiver and test barrel for one gauge. Still kinda pricey for a guy that just wants to have some fun and satisfy his curiosity.

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MaximumSmoke
PostPosted: Mon Jan 03, 2022 9:31 am  Reply with quote
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MSM2019 --

Does one have to use cylinder choke (no choke) for good comparative results?

I have the RSI strain gage pressure testing system but have been hang-firing for a long time on using it. I intend to use the system for comparative testing and verification of loads appropriate to my very light-barreled 16 gauge damascus hammer gun which has a 65 mm chamber and virtually no forcing cone. I have adapted an old single-shot barrel (H&R or Iver Johnson?) with 2 9/16 inch chamber and also no forcing cone I can see, to fit on a fairly modern Stevens single-shot action. It has internal dimensions very close to those of the old hammer gun. I will eventually strain gage it at several distances down the barrel, starting at 1 inch from the breech face, à la the way Sherman Bell did it for his comparisons of internal ballistics of black and smokeless powder loads having equivalence of exterior ballistics.

I cannot recall the chokes of my hammer gun, but I'm betting they are tight. Would it be best if I took all the choke out of that full-choked single-shot test barrel?

I intended (and still do) to send to Armbrust for testing, the prospective loads as well as a couple of loads that would bracket the loads intended for that damascus hammer gun -- probably one around 10 to 11 Ksi, and one around the 5 Ksi range. That might take some experimentation to arrive at loads of those pressures that have consistent stats -- pressure and velocity variations, extreme and standard. That would give me at least 3 Armbrust-verified strain vs. pressure points from which I can see how true and linear the calculations of pressure vs. strain from the thick-walled cylinder equations are for my test gun. http://courses.washington.edu/me354a/Thick%20Walled%20Cylinders.pdf

From there, and keeping my own store of very carefully made reference ammo, I hope to be able to trust my ballistic quantifications of various loads, and verify I'm still making safe loads as the future brings variations in powder batches, primers, and for different shot sizes. Shot size should be a minor effect, as the range will likely only include 9's to 6's. I presume I will always use lead shot, but you never know what the future will bring.

Anyway, Mark, I'd appreciate your perspective on the cylinder choke issue, as I have a couple of choices: 1) make my "pressure gun" conform closely to what Armbrust or the industry uses, or 2) make it conform more closely to my old damascus gun. I guess one question is how choke in a 28 or 30 inch barrel affects internal ballistics. I think choke tends to increase velocity, right? Thanks for whatever you can relate.

Cheers, Happy Hunting, and Happy New Year!
Tony
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MSM2019
PostPosted: Mon Jan 03, 2022 11:14 am  Reply with quote



Joined: 04 Mar 2019
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Location: Central ND

Hi Tony,

When you are using a skyscreen or Infra-red chronograph, cylinder choke gives you the most accurate velocities. The more constriction the higher the recorded velocity.

That does not hold true for the induction coil type chronographs, they normally use full chokes with that system.

Chokes have no effect on internal bore pressures. However the industry does use a strain gauge(s) at the choke for firearms and ammunition design purposes.

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MSM2019
PostPosted: Mon Jan 03, 2022 11:33 am  Reply with quote



Joined: 04 Mar 2019
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Location: Central ND

Tony,

As far as making a "pressure gun". That is tough, and probably not necessary.

On their website, SAAMI has all the dimensions for a test barrel. I would guess that you could use a barrel that would fit those tolerances as close as possible. All of Tom Armbrust's barrels are proper test barrels.

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Brewster11
PostPosted: Tue Jan 04, 2022 12:35 pm  Reply with quote



Joined: 08 Feb 2009
Posts: 1301
Location: Western WA

Mark
The strain gauge approach seems quite feasible. What type of computer I/O device is needed to connect the strain gauge to a PC? It would also seem that some software might be needed as well. Maybe that’s what the PT II system contains.
Thanks
B.
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