Ballistic testing- strain gauge

[Dogchaser37]

Hi I am Mark M.

New here and just looking for information about testing chamber pressures using a strain gauge or possibly the RSI Pressure Trace II system.

I understand that there is a gentleman by the name of Larry Gibson that might have some experience in this area.

Thanks in advance for any help offered.

Mark

[megasupermagnum]

Larry uses a different brand of system, but the principle is basically the same. I have the Pressure Trace II system. My advice is don't look to the internet for answers. The guys who developed the Pressure Trace II are more than knowledgeable. Every question you can possibly have is in the operating manual, but it can be tough to digest. In that case, a call to them is the way to go.

If you are simply looking to see it in action, I often shoot in Hecla, which is right against the SD/ND border. You are welcome to try mine out.

[Newboy]

Using strain gauges is good tool, but the results are merely comparative pressures. I have never seen anyone calibrate any system to give quantitative results.

Firing a factory cartridge and assuming it's pressure is not a calibration!


Sent from my iPhone using Tapatalk Pro

[megasupermagnum]

Using strain gauges is good tool, but the results are merely comparative pressures. I have never seen anyone calibrate any system to give quantitative results.

Firing a factory cartridge and assuming it's pressure is not a calibration!


Sent from my iPhone using Tapatalk Pro

That's nonsense. All you need is a load you know the pressure of. Pressure Trace II has a way to calibrate based off that. Technically you are calibrating based off another test gun, and their calibration, so I guess you are half right. What matters most is that the measurements you input are dead on. If your barrel OD, ID, and case wall thickness are entered accurately, then I've found little reason to mess with calibration. Weather is a much bigger concern. I'm not sure how you could reasonably pressure test when it's -10 out, no matter the calibration.

[Petander]

A tungsten shot vendor / ammo manufacturer is using Pressure Trace here in Finland. They also provide pressure testing service.

I've been drooling the system for years...

If it's good enough for making commercial ammo, it is good enough fo me as well.

http://www.ammox.fi/latauspaketit.html

[Dogchaser37]

Thanks megasupermagnum. I am leaning towards the Pressure Trace II as it is all there and pretty much ready to go. What do you use for a computer?

True you can't calibrate the Pressure Trace II, but you can't calibrate the SAAMI piezoelectric transducer system either. Which means you have to have reference ammunition. Not really a huge issue. My use for this system is shotshells and it is reasonably easy to have ammo tested and assigned pressure and velocity values, which you than use to correct for any differences between what your system reads and the assigned values.

[Larry Gibson]

I have both the Oehler M43 and a Pressure Trace II system. I've 15 years' experience with the M43 PBL having tested thousands of rounds of many different out of 30+ different test firearms.

megasupermagnum is correct, the Pressure Trace operating manual (available online at their site) is a treasure trove of information regarding ballistic test. Suggest you go to their site, download the manual and read it. I will be glad to answer any questions then.

[Larry Gibson]

Using strain gauges is good tool, but the results are merely comparative pressures. I have never seen anyone calibrate any system to give quantitative results.

Firing a factory cartridge and assuming it's pressure is not a calibration!


Sent from my iPhone using Tapatalk Pro

Yes, strain gauge measuring is a good tool. The use of "reference ammunition" is the industry standard to "calibrate" the various test fixtures used by various manufacturers. The Oehler M83 is more often used by many manufacturers of ammunition also.

You might want to go to the SAAMI site and read their manual, specifically the use of reference ammunition to calibrate pressure test fixtures. The use of reference ammunition is industry standard because the pressure of the reference ammunition is known. When fired in a test fixture, which probably will give a different pressure, the difference between the two pressures gives a "correction factor" which is then used through further testing with that test barrel. It is how it is done contrary to what many think and most internet rumors.

I use factory ammunition to "calibrate" my own test barrels. I have gotten the tested pressure of the lot numbers of that ammunition from the manufacturers. I've also duplicated loads from manuals that list complete details of the load components along with their psi measurement of that load. It is surprising how close they can be.

As to 'comparative pressures? that is correct. But you have to remember that pressures listed by the major manufacturers are also simply comparative. When you look at factory or loading manual listed pressures from the test fixtures (simply a different type of firearm) they are simply "comparative" to any other firearm.

Also do not believe that all factory ammunition is loaded to the SAAMI MAP for that cartridge. Some are but most are not. If you further read the SAAMI manual, you will see the "standard" to which factory ammunition is loaded. Maybe you shouldn't read it, it might just disappoint you.

[Dogchaser37]

Thanks Larry. On my way to the RSI site.

[missionary5155]

Thank you Larry. That explained alot to me in a very easy to understand way.

[popper]

Strain gauges are easy to calibrate. Your electronic scale uses one. What is difficult is translating that 'calibration' over to your barrel. Piezos are only good for transient stuff. Been used in fish finders for a long time.

[megasupermagnum]

Thanks megasupermagnum. I am leaning towards the Pressure Trace II as it is all there and pretty much ready to go. What do you use for a computer?

True you can't calibrate the Pressure Trace II, but you can't calibrate the SAAMI piezoelectric transducer system either. Which means you have to have reference ammunition. Not really a huge issue. My use for this system is shotshells and it is reasonably easy to have ammo tested and assigned pressure and velocity values, which you than use to correct for any differences between what your system reads and the assigned values.

It's no different than calibrating a scale with a standard. The only difference is your standard ammunition is subject to a whole bunch of variability. I don't do much with rifles, since they show good pressure signs, and ultimately are not that hard to load for. I use my system mostly for shotguns, which have no pressure signs, and a million variables. The good thing there is you can send some ammo off to Tom Armbrust for testing, and calibrate to his setup. In the settings there is an input I think called offset. You can adjust the program by how far off the pressure is from what it should read. The only caveat is that you have to calibrate when it is about the same temperature as he did. After that first calibration, I don't see any reason to shoot standard loads, as the different weather will effect your results. You will know if your system is working right by getting good smooth pressure curves.

I use a Lenovo thinkpad. I have no idea how the system works on MAC. Just about any Microsoft laptop will work. The system needs bluetooth to read, but you can buy cheap little dongles that do that if it doesn't already. Pretty much any computer built in the last 10 years should have bluetooth.

[Dogchaser37]

Thanks megasupermagnum, I am all set with the computer also. The RSI website was informative. When the weather warms up a bit, you know what I will be doing.

BTW Do I recognize your username from either SGW or 16ga.com?

[megasupermagnum]

Thanks megasupermagnum, I am all set with the computer also. The RSI website was informative. When the weather warms up a bit, you know what I will be doing.

BTW Do I recognize your username from either SGW or 16ga.com?

I do have an account on shotgun world, but it has been quite some time since I posted there. It's kind of an uppidy, game-shooter atmosphere, where trying to ask about loading hunting loads will not get a good answer. I have been on 16ga, not so much this past year. I made an informal test for myself, hunting the entire year with a 10 gauge muzzleloader for all small game. That's exactly what I did. I killed a spring turkey, a handful of squirrel and rabbits, a ton of ducks and geese, pheasant, and hopefully yet a winter turkey, all with that one muzzleloading shotgun. My 16 gauge 11-48 sits in the safe, but I did shoot a black bear with it in September. 16ga is a good site, although they are a bit uptight about working with different 16 gauge loads beyond the norm. There is one member on that site that is more knowledgeable than me about 16 gauge's by far, but he too is somewhat stuck in his way. Still a great source of info. I think his username started with MSM by coincidence. I love the 16 gauge for what it is, a light little gun with a big bore, but I'm not afraid to do different things. Besides normal lead shot loads, I'm always playing with bismuth, obviously figured out a good slug load for bears, buckshot. You always see how a 16 gauge is useless with more than 1 1/8 oz of shot. I always figured you couldn't fit much more. Well as it is, I've got some 1 5/8 oz turkey loads ready to pressure test, so space is no concern at all.

[Dogchaser37]

Thanks......MSM2019 is my username on 16ga.com. I do my best. I am here because I was told that there were folks here that knew about using strain gauges. I want to do some stuff but sending ammo to be tested is too much time wasted and gets expensive. I only hunt with a 16 unless it is the rare waterfowl hunt. I love the gauge. Took 3 turkeys, sharptails, huns and pheasant with it this year. Had a blast with my young GSP, he is really coming into his own. My female GSP, she's about 7.5 now did a nice job too. All my best and thanks to everyone here.

[megasupermagnum]

You are the the one I was thinking of. I'm not sure there's much I can do for you about 16 gauges that you don't already know, but I'll gladly help on the Pressure Trace II if I can.

[Dogchaser37]

Talking about loads for the 16 gauge. I came up with some ideas awhile back and made a nice buffered bismuth load, which lead to a steel load, which lead to a buffered 1 1/4 oz. lead turkey load, which ended up with a buffered 1 1/4 oz. of 5's for pheasant. You are correct, there is plenty of room in the hull for a larger payload. I used Steel powder for the loads I just mentioned. That is some of the stuff I want to work with and the reason why I inquired about the strain gauge stuff. I always wanted the piezo setup complete with universal receiver and test barrels, but that idea went out the window with prices being about $15000+ for one gauge. Just too much for a guy that wants to play now and then.

[megasupermagnum]

Yeah, I was blown away when I saw the Pressure Trace was only $600. I see it is now $750, but still a good deal when it was $50 a pop to have a load tested by Tom Armbrust, and that's probably more now too. I've been very pleased with the system. It's not perfect, but it does what it says it will. About my only complaint is that the strain gauge wires are delicate. They have to be, else you'd have a giant thing on your barrel. Those gauges are the big cost, as they are not reusable. I like to use the 3" jumper wire they sell, it adds freedom so you aren't pulling on the tiny strain gauge wires. I then duct tape the main cable right to the barrel. Yes, duct tape. There's probably more elaborate ways to do it, but I just stick it on there, and it doesn't' move. They send a little Velcro strap with, but I couldn't get it to hold, and recoil caused the wire to move around too much. Attaching the strain gauges to the barrels is simple enough, just a little tricky. You only get one shot at it, so if you don't get it right, you just threw away that money. So far I've only lost one because I accidentally glued my finger to the wire, and tore the wire off. Speaking of which, these strain gauges will be on the barrel permanently. You can take them off with some acetone, but you can't reuse them. You can still hunt with them on there, but if you snag that tiny wire, you will ruin the gauge. What I did was dedicate a gun or barrel for each. In 12 gauge I use a Mossberg 500 barrel that I don't use for anything else. In 16 gauge I use a Stevens 506a that I don't like that much. In 10 gauge I use a barrel that I don't intend on using much, only for deer hunting which isn't hard on guns.

I had no problems with computer setup, but being a Millennial, I was born with that ability. The way this system works is that you have the program on your laptop, which you download from their CD. The Pressure Trace II itself is in a yellow Pelican case, which connects to your PC wirelessly with bluetooth. That's probably the toughest part for most people. From the yellow box, a cable runs to your gun, specifically the strain gauge. If it is a sunny day, seeing the screen of your computer can be tough. Usually I drape a shirt over my head to see.

So ultimately what you have is a system that cost as much or less as a decent shotgun, is surprisingly precise, but the handicaps are you have a delicate strain gauge that is permanently attached to something, and because of weather, ammo, and other variables can't be as accurate as what the labs do. If you could shoot in your heated garage year round, you could probably do some really good work with one. Even outdoors, I find mine a very valuable tool. I still use load data as best I can to estimate, but this system is a million times better than guessing.

[Dogchaser37]

I could probably shoot in my garage as it is heated, but not so sure my better half would care for the noise. If you were to send Tom Armbrust, because I know he uses SAAMI reference ammunition, some loads and told him what you were doing with them you would have some pretty good in house reference of your own. The loads would have to be something like a 1 oz. target load, 1 1/4 oz. heavy lead(maybe buffered) and maybe a steel shot or Bismuth load or something really heavy like that 1 5/8 oz. load. That would cover the 16 gauge pretty well, just depends on what loads you want to develop. Some folks think a target load is enough, but it really isn't. Look at the SAAMI reference load section, that may give you some ideas. With actual reference loads you know that you will be on the money with your pressures.

[Dogchaser37]

As far as guns, I am going to buy another barrel for a 16 gauge 870 I already have, that way I don't have to be so careful. I use the 870 for turkey hunting.

[LaPoint]

Thanks Dogchaser37 & Megasupermagnum for discussing the Pressure Trace system. I have looked at them but haven't been willing to spend the $$. I think that you may have pushed me over the edge. On a side note-- Dogchaser37 I have a sweet spot for GWPs. I had a small male for almost 15 yrs. He was the most versatile hunting dog I've ever hunted behind. He was a great family pet and too smart for his own good sometimes but we loved him dearly. He passed a little over a year ago and still miss him daily.

[megasupermagnum]

You don't need, or even want multiple rounds for calibration. You can read about the specifics in the PTII manual. What is very important is that you have your barrel inputs correct. The OD of the barrel is easy, just measure the exact spot you put the strain gauge. The ID of the chamber is a little tougher, but I simply slug it with a lead ball. Even being off .002" makes a difference, so you can't guess on this at all. If you do that right, calibration is more or less just checking to make sure it is reading right.

[Larry Gibson]

With a new test barrel or if a new strain gauge in installed I run a 10 shot test of the reference ammunition/load i have for that barrel/cartridge. Pressure tests, like chronograph tests, will give a different average psi even if tests are conducted back to back with the same ammunition. Also, the variation will and can seem a bit large as compared to average fps variation. If all checks out with the reference being close to the expected psi then we can compute a correction factor. I will occasionally then shoot a 3 or 5 shot test of the reference ammunition/load, especially if the test barrel hasn't been used in a while. If the average psi falls within the ES psi of the original 10 shot test, then the test barrel is good to go.

Just a couple days ago I pressure tested some 35 Rem loads in my M91 Mauser with Shilen barrel. I had not shot that rifle in well over 2 years, so I ran a six shot test out of the last box of Federal 35 rem PowerShok. The average psi was 1,800 psi over the previous test almost 5 years ago. I also tested a carefully duplicated load from Lyman's 50th manual with everything the same as in the manual except the 200 gr J bullet. Lyman used a 200 gr FTX which as seated quite deep, and I used a 200 gr Rem CorLok which was seated to the bottom of the case neck. Because of the small 35 Rem case i expected a slightly lower psi than the 32,400 psi Lyman listed with the FTX bullet. And so it was, my load with the Remington bullet ran 2,000 psi less. Also different conditions can make that much difference also. That's why it is also imperative to enter the conditions for each test into the computer program. You can do that with both the M43 PBL and the Pressure Trace II. Thus, the test barrel was reading what it should have within test parameters.

Now some may think that is an awful lot of difference and it does seem so. However, it is not. Anyone familiar with pressure testing and having enough experience at such will quickly understand that. It is why SAAMI lists not only a MAP for each cartridge but also a MPLM, a MPSM and MEV can be calculated. Let me add that pressure measurements are not as "precise" as many, if not most, think.

[megasupermagnum]

I was going to ask you how you deal with the winter temperatures Larry, but I forgot you are down in paradise. If the weather there is anything like the few times I've been to Yuma in the winter, it's probably a beautiful 70-75 there, might even need a long sleeve shirt. I guess a better question is how do you deal with your summer temperatures when it's 100 every day?

[Stockcarver]

Fun stuff. Photos from some 25 years ago. A 50 cal cartridge putting out about 5500 ft/lbs for a lever gun project. Hundreds of test rounds through the M98 test gun.

https://i.imgur.com/ogZVN2s.jpg

https://i.imgur.com/hka6Py0.jpg

https://i.imgur.com/SiVzIcU.jpg?1

https://i.imgur.com/Ukt6wmA.jpg

https://i.imgur.com/cqKfMya.jpg

https://i.imgur.com/EDfbpF3.jpg

50 cal is the top rifle

https://i.imgur.com/0ppHxly.jpg?2

[Larry Gibson]

I was going to ask you how you deal with the winter temperatures Larry, but I forgot you are down in paradise. If the weather there is anything like the few times I've been to Yuma in the winter, it's probably a beautiful 70-75 there, might even need a long sleeve shirt. I guess a better question is how do you deal with your summer temperatures when it's 100 every day?

In the summer with temps of 85 - 110 [it does get hotter, but I don't test on those days] I get to the range about 45+ minutes before shooting light and get set up. That way at first shooting light (when the Sky Screens will function) I'll shoot a test (usually 10 shots) with 2 minutes between shots. I have a small air pump I blow the hot gas out of the barrel with right after the test shot. Then I will shoot a second rifle off another bench for 10 minutes or so letting the test rifle "cool" a bit before shooting another test. I'll stop testing when the temp hits 100 in the shade. That usually gives me about 2 - 3 hours of test time.

Then I'm back home, clean the guns, print out the data sheets, put the equipment away, hit the pool, have a marguerita, take a nap, hit the pool, have a marguerita, take a nap, etc.......it's tough but I struggle through it.....[smilie=l:

[toot]

Welcome.

[Larry Gibson]

stockcarver

Nice test fixture. should be easy to switch barrels and even bolts for different cartridges. Too bad we didn't get together for some testing and shooting when I lived up in Tacoma area.

[Dogchaser37]

Cool stuff, if I ever decide to take up centerfire shooting in earnest, I will come back to this forum. Thanks everyone!!

[megasupermagnum]

My first memory of Arizona was getting off a plane in Phoenix. We left Minneapolis when it was reasonably warm, maybe 15 degrees in December. I took one step out of the airport in Phoenix at midnight, and I was blasted with 80 degree hot air. Still it wasn't as bad as the time I went to Miami, and thought I was going to choke on the air. Actually Arizona is one of the most pleasant places I've been, although I could never handle that heat. South Dakota hit 107 this summer, and that was one of the most oppressive things I've ever experienced. I really feel for those in the humid NW that got to feel 115 in that tropic jungle.