Custom action pressure ceiling.
- Thread starter RockyMtnMT
- Start date
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I'm not the best with numbers but if you posted 10 posts a day on gun forums wouldn't that be like 3,650 posts a year ? I just noticed you joined this site in 2006 . How many posts ?
Clark
Well-Known Member
- Joined
- Oct 19, 2006
- Messages
- 772
I started posting on rec.guns in the mid 90's, before the www sites got going.
Here is a post from rec.guns:
rec.guns | Google Groups
Now I have joined ~ 100 forums, but only post on a few.
Nice to meet you clark I was just poking. you've probably forgot more than i'll ever know
BigBuck
He didn't say he'd been on LRH that long. Probably posted on other/older shooting forums before joining LRH. Just an observation on my part.
Clark
Well-Known Member
- Joined
- Oct 19, 2006
- Messages
- 772
Oldie but good, from 1997 "Bert Bobbit [sic] with his Krieger Barrelled PALMA rifle.":
rec.guns | Google Groups
rec.guns | Google Groups
bigngreen
Well-Known Member
Clark could you clarify this for me? I have been interested in the RSI set up and would be interested in some info or any thoughts you might have.
Thanks
Clark
Well-Known Member
- Joined
- Oct 19, 2006
- Messages
- 772
The accuracy of a strain gauge on your rifle cannot be calculated, as you can not accurately measure the location of the bonding, the orientation of the bonding, or the quality of the bonding.
The formula for a threaded and screwed barrel pressure vs strain in not in Roark's book.
The math would be impossibly difficult.
If you use calibration ammo, you must find it's traceability to NIST and it's inaccuracy. Plus there is the error when shot in your chamber, which cannot be quantified.
A measurement of unknown accuracy has no value.
Finally if you did have an accurate measurement of peak psi in your chamber, what would you do with it?
To have meaning you must compare it to something.
You might say SAAMI registered peak average pressures, but how those were chosen is demonstrably capricious.
In the strong action the real question is threshold of brass life.
You have the answer in your hand, and to purse a strain gauge option is taking leave of the senses.
Sure, if you are going to sell ammo for the wide variety of guns it may be used in, you must have a pressure standard. Ballisticians have traditionally shipped ammo back and forth to get consensus, and did not have calibrators traceable to NIST.
But for the individual handloader, loading his own ammo, he has direct access to the goal information, what is the threshold of long brass life.
How did the Germans get 2900 fps 150 gr 8x57mm in 1905?
It was not based on how strong the actions were, it was based on the strength of the Mauser case head.
Try to make one of those old Mausers go faster than 2900 fps, and you will see that it is already up against the threshold of long brass life.
Many years later SAAMI may have registered that kind of pressure for the Mauser case head in the 270, but they did not for the 8mm.
So if you had a strain gauge on an 8mm what is your goal pressure?
You would not want to feel stupid for buying it so you would have to play with it somehow.
Maybe workup a load to the threshold of long brass life, and then measure that pressure.
You could then say that pressure is your goal.
Kind of like shooting arrows into the fence and then painting a bullseye around them.
The formula for a threaded and screwed barrel pressure vs strain in not in Roark's book.
The math would be impossibly difficult.
If you use calibration ammo, you must find it's traceability to NIST and it's inaccuracy. Plus there is the error when shot in your chamber, which cannot be quantified.
A measurement of unknown accuracy has no value.
Finally if you did have an accurate measurement of peak psi in your chamber, what would you do with it?
To have meaning you must compare it to something.
You might say SAAMI registered peak average pressures, but how those were chosen is demonstrably capricious.
In the strong action the real question is threshold of brass life.
You have the answer in your hand, and to purse a strain gauge option is taking leave of the senses.
Sure, if you are going to sell ammo for the wide variety of guns it may be used in, you must have a pressure standard. Ballisticians have traditionally shipped ammo back and forth to get consensus, and did not have calibrators traceable to NIST.
But for the individual handloader, loading his own ammo, he has direct access to the goal information, what is the threshold of long brass life.
How did the Germans get 2900 fps 150 gr 8x57mm in 1905?
It was not based on how strong the actions were, it was based on the strength of the Mauser case head.
Try to make one of those old Mausers go faster than 2900 fps, and you will see that it is already up against the threshold of long brass life.
Many years later SAAMI may have registered that kind of pressure for the Mauser case head in the 270, but they did not for the 8mm.
So if you had a strain gauge on an 8mm what is your goal pressure?
You would not want to feel stupid for buying it so you would have to play with it somehow.
Maybe workup a load to the threshold of long brass life, and then measure that pressure.
You could then say that pressure is your goal.
Kind of like shooting arrows into the fence and then painting a bullseye around them.
Fitch
Well-Known Member
It is not true that a measurement of unknown accuracy is of no value. It is also not true that the accuracy of the PT unit can't be extabilshed within reasonable limits. The copper crusher measurement system used by industry for decades turned out to be useful and to have almost no relationship to what they thought they were measuring.
For engineering purposes, or to be useful for some load development, it doesn't have to be perfectly accurate, and there doesn't have to be a pressure goal to make pressure instrumentation useful. The ammo industry went for decades using copper cursher testing that they didn't even understand and it was useful. Used on a test barrel of specified geometry, the Pressure Trace system is better than the copper crusher. Located with due consideration for geometry and checked with some factory ammo, it can be close enough to be useful as an engineering tool for a guy trying to get a better understanding of what's happening.
I'm an engineer. I spent 35 years in Aerospace mostly figuring out how to do what had never been done before. We did all sorts of experiments and simulations to "engineering" accuracy. Worked pretty well for gaining an understanding of what's going on.
If barrel exit time is of interest, the PT system will allow measuring it. If one is working on reduced or subsonic loads, the PT system can be useful for making sure there is enough margin in the load to assure the bullet won't stick. It can provide assurance there are so secondary detonation issues with a reduced load.
I could make the argument that using the PT as an engineering tool in conjunction with QuickLoad is potentially more useful for developing hunting loads than intentionally proving over and over and over thousands of times that it's possible to exceed the pressure of the brass. I see little value in that unless it leads to better brass for your rifle, which so far doesn't seem to have been the case.
That said, while I do use QuickLoad a lot, I don't see the need for a PT unit for developing hunting loads, nor do I see any reason to develope an inordinate fixation on blowing up brass for developing hunting loads. Blowing up brass seems to have become an end in and of itself. If it feels good, do it, but I don't see any benefit from proving the obvious over and over again.
Fitch
Folks interested in the technical aspects of pressure testing should get a copy of ANSI/SAAMI document Z299.4-T992, "Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Rifle Sporting Ammunition for the Use of Commercial Manufacturers." It's an eye-opener for 99% of reloaders. SAAMI's web site used to have it available for public download but I think they stopped that. They also had similar documents for rimfire and pistol ammo, ammo, primer and powder storage, primer and powder caused fires.
I'll see if LRH has a place to put them, then I'll upload 'em there for all to obtain. Each time someone accesses and downloads them, there'll be an automatic link made to bank accounts of folks who get them that'll alert me to who did it so I can sent them a thank-you card for doing it after appropriate funds are transferred to my bank account. There's been some glitches in that software and it usually doesn't work.
I'll see if LRH has a place to put them, then I'll upload 'em there for all to obtain. Each time someone accesses and downloads them, there'll be an automatic link made to bank accounts of folks who get them that'll alert me to who did it so I can sent them a thank-you card for doing it after appropriate funds are transferred to my bank account. There's been some glitches in that software and it usually doesn't work.
